diff --git a/core/lib/Drupal/Core/Theme/MissingThemeDependencyException.php b/core/lib/Drupal/Core/Theme/MissingThemeDependencyException.php
new file mode 100644
index 0000000..c3f72af
--- /dev/null
+++ b/core/lib/Drupal/Core/Theme/MissingThemeDependencyException.php
@@ -0,0 +1,48 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Theme\MissingThemeDependencyException.
+ */
+
+namespace Drupal\Core\Theme;
+
+/**
+ * Exception to be thrown when base theme for installed theme is not installed.
+ *
+ * @see \Drupal\Core\Theme\ThemeInitialization::getActiveThemeByName().
+ * @see \Drupal\system\Controller\DbUpdateController::ensureActiveThemeDependencies().
+ */
+class MissingThemeDependencyException extends \Exception {
+
+  /**
+   * The missing theme dependency.
+   *
+   * @var string
+   */
+  protected $theme;
+
+  /**
+   * Constructs the exception.
+   *
+   * @param string $message
+   *   The exception message.
+   * @param string $theme
+   *   The missing theme dependency.
+   */
+  public function __construct($message, $theme) {
+    parent::__construct($message);
+    $this->theme = $theme;
+  }
+
+  /**
+   * Gets the machine name of the missing theme.
+   *
+   * @return string
+   *   The machine name of the theme that is missing.
+   */
+  public function getMissingThemeName() {
+    return $this->theme;
+  }
+
+}
diff --git a/core/lib/Drupal/Core/Theme/ThemeInitialization.php b/core/lib/Drupal/Core/Theme/ThemeInitialization.php
index 95f27a9..e1cd44c 100644
--- a/core/lib/Drupal/Core/Theme/ThemeInitialization.php
+++ b/core/lib/Drupal/Core/Theme/ThemeInitialization.php
@@ -109,6 +109,16 @@ public function getActiveThemeByName($theme_name) {
     $ancestor = $theme_name;
     while ($ancestor && isset($themes[$ancestor]->base_theme)) {
       $ancestor = $themes[$ancestor]->base_theme;
+      if (!$this->themeHandler->themeExists($ancestor)) {
+        if ($ancestor == 'stable') {
+          // Themes that depend on Stable will be fixed by system_update_8012()
+          // and system_update_8014(). There is no harm in not adding it as an
+          // ancestor since at worst some people might experience slight visual
+          // regressions on the update.php
+          continue;
+        }
+        throw new MissingThemeDependencyException(sprintf('Base theme %s has not been installed.', $ancestor), $ancestor);
+      }
       $base_themes[] = $themes[$ancestor];
     }
 
diff --git a/core/lib/Drupal/Core/Theme/ThemeInitializationInterface.php b/core/lib/Drupal/Core/Theme/ThemeInitializationInterface.php
index f2b1547..cd5c1be 100644
--- a/core/lib/Drupal/Core/Theme/ThemeInitializationInterface.php
+++ b/core/lib/Drupal/Core/Theme/ThemeInitializationInterface.php
@@ -34,6 +34,9 @@ public function initTheme($theme_name);
    *
    * @return \Drupal\Core\Theme\ActiveTheme
    *   An active theme object instance for the given theme.
+   *
+   * @throws \Drupal\Core\Theme\MissingThemeDependencyException
+   *   Thrown when base theme for installed theme is not installed.
    */
   public function getActiveThemeByName($theme_name);
 
diff --git a/core/modules/config/src/Tests/ConfigImportInstallProfileTest.php b/core/modules/config/src/Tests/ConfigImportInstallProfileTest.php
index 19ef2ee..e15d3ac 100644
--- a/core/modules/config/src/Tests/ConfigImportInstallProfileTest.php
+++ b/core/modules/config/src/Tests/ConfigImportInstallProfileTest.php
@@ -67,6 +67,7 @@ public function testInstallProfileValidation() {
     $core['module']['testing_config_import'] = 0;
     unset($core['module']['syslog']);
     unset($core['theme']['stark']);
+    $core['theme']['stable'] = 0;
     $core['theme']['classy'] = 0;
     $sync->write('core.extension', $core);
     $sync->deleteAll('syslog.');
diff --git a/core/modules/system/src/Tests/Theme/StableLibraryOverrideTest.php b/core/modules/system/src/Tests/Theme/StableLibraryOverrideTest.php
new file mode 100644
index 0000000..526be51
--- /dev/null
+++ b/core/modules/system/src/Tests/Theme/StableLibraryOverrideTest.php
@@ -0,0 +1,185 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\system\Tests\Theme\StableLibraryOverrideTest.
+ */
+
+namespace Drupal\system\Tests\Theme;
+
+use Drupal\simpletest\KernelTestBase;
+
+/**
+ * Tests Stable's library overrides.
+ *
+ * @group Theme
+ */
+class StableLibraryOverrideTest extends KernelTestBase {
+
+  /**
+   * The theme manager.
+   *
+   * @var \Drupal\Core\Theme\ThemeManagerInterface
+   */
+  protected $themeManager;
+
+  /**
+   * The theme initialization.
+   *
+   * @var \Drupal\Core\Theme\ThemeInitializationInterface
+   */
+  protected $themeInitialization;
+
+  /**
+   * The library discovery service.
+   *
+   * @var \Drupal\Core\Asset\LibraryDiscoveryInterface
+   */
+  protected $libraryDiscovery;
+
+  /**
+   * A list of all core modules.
+   *
+   * @var string[]
+   */
+  protected $allModules;
+
+  /**
+   * A list of libraries to skip checking, in the format extension/library_name.
+   *
+   * @var string[]
+   */
+  protected $librariesToSkip = [];
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setUp() {
+    parent::setUp();
+
+    $this->themeManager = $this->container->get('theme.manager');
+    $this->themeInitialization = $this->container->get('theme.initialization');
+    $this->libraryDiscovery = $this->container->get('library.discovery');
+
+    $this->container->get('theme_installer')->install(['stable']);
+
+    // Enable all core modules.
+    $all_modules = system_rebuild_module_data();
+    $all_modules = array_filter($all_modules, function ($module) {
+      // Filter contrib, hidden, already enabled modules and modules in the
+      // Testing package.
+      if ($module->origin !== 'core' || !empty($module->info['hidden']) || $module->status == TRUE || $module->info['package'] == 'Testing') {
+        return FALSE;
+      }
+      return TRUE;
+    });
+    $this->allModules = array_keys($all_modules);
+    sort($this->allModules);
+    $this->enableModules($this->allModules);
+  }
+
+  /**
+   * Ensures that Stable overrides all relevant core library assets.
+   */
+  public function testStableLibraryOverrides() {
+    // First get the clean library definitions with no active theme.
+    $libraries_before = $this->getAllLibraries();
+    $libraries_before = $this->removeVendorAssets($libraries_before);
+
+    $this->themeManager->setActiveTheme($this->themeInitialization->getActiveThemeByName('stable'));
+    $this->libraryDiscovery->clearCachedDefinitions();
+
+    // Now get the library definitions with Stable as the active theme.
+    $libraries_after = $this->getAllLibraries();
+    $libraries_after = $this->removeVendorAssets($libraries_after);
+
+    $root = \Drupal::root();
+    foreach ($libraries_before as $extension => $libraries) {
+      foreach ($libraries as $library_name => $library) {
+        // Allow skipping libraries.
+        if (in_array("$extension/$library_name", $this->librariesToSkip)) {
+          continue;
+        }
+        $library_after = $libraries_after[$extension][$library_name];
+
+        // Check that all the CSS assets are overridden.
+        foreach ($library['css'] as $index => $asset) {
+          $clean_path = $asset['data'];
+          $stable_path = $library_after['css'][$index]['data'];
+          // Make core/misc assets look like they are coming from a "core"
+          // module.
+          $replacements = [
+            'core/misc/' => "core/modules/core/css/",
+          ];
+          $expected_path = strtr($clean_path, $replacements);
+
+          // Adjust the module asset paths to correspond with the Stable folder
+          // structure.
+          $expected_path = str_replace("core/modules/$extension/css/", "core/themes/stable/css/$extension/", $expected_path);
+          $assert_path = str_replace("core/modules/$extension/", '', $clean_path);
+
+          $this->assertEqual($expected_path, $stable_path, "$assert_path from the $extension/$library_name library is overridden in Stable.");
+        }
+      }
+    }
+  }
+
+  /**
+   * Removes all vendor libraries and assets from the library definitions.
+   *
+   * @param array[] $all_libraries
+   *   An associative array of libraries keyed by extension, then by library
+   *   name, and so on.
+   *
+   * @return array[]
+   *   The reduced array of libraries.
+   */
+  protected function removeVendorAssets($all_libraries) {
+    foreach ($all_libraries as $extension => $libraries) {
+      foreach ($libraries as $library_name => $library) {
+        if (isset($library['remote'])) {
+          unset($all_libraries[$extension][$library_name]);
+        }
+        foreach (['css', 'js'] as $asset_type) {
+          foreach ($library[$asset_type] as $index => $asset) {
+            if (strpos($asset['data'], 'core/assets/vendor') !== FALSE) {
+              unset($all_libraries[$extension][$library_name][$asset_type][$index]);
+              // Re-key the array of assets. This is needed because
+              // libraries-override doesn't always preserve the order.
+              if (!empty($all_libraries[$extension][$library_name][$asset_type])) {
+                $all_libraries[$extension][$library_name][$asset_type] = array_values($all_libraries[$extension][$library_name][$asset_type]);
+              }
+            }
+          }
+        }
+      }
+    }
+    return $all_libraries;
+  }
+
+  /**
+   * Gets all libraries for core and all installed modules.
+   *
+   * @return array[]
+   *   An associative array of libraries keyed by extension, then by library
+   *   name, and so on.
+   */
+  protected function getAllLibraries() {
+    $modules = \Drupal::moduleHandler()->getModuleList();
+    $module_list = array_keys($modules);
+    sort($module_list);
+    $this->assertEqual($this->allModules, $module_list, 'All core modules are installed.');
+
+    $libraries['core'] = $this->libraryDiscovery->getLibrariesByExtension('core');
+
+    $root = \Drupal::root();
+    foreach ($modules as $module_name => $module) {
+      $library_file = $module->getPath() . '/' . $module_name . '.libraries.yml';
+      if (is_file($root . '/' . $library_file)) {
+        $libraries[$module_name] = $this->libraryDiscovery->getLibrariesByExtension($module_name);
+      }
+    }
+    return $libraries;
+  }
+
+}
diff --git a/core/modules/system/src/Tests/Update/UpdatePathRC1TestBaseTest.php b/core/modules/system/src/Tests/Update/UpdatePathRC1TestBaseTest.php
index 47e70b1..54c2d1e 100644
--- a/core/modules/system/src/Tests/Update/UpdatePathRC1TestBaseTest.php
+++ b/core/modules/system/src/Tests/Update/UpdatePathRC1TestBaseTest.php
@@ -34,6 +34,8 @@ protected function setDatabaseDumpFiles() {
    * Tests that the database was properly loaded.
    */
   public function testDatabaseLoaded() {
+    $extensions = \Drupal::service('config.storage')->read('core.extension');
+    $this->assertFalse(isset($extensions['theme']['stable']), 'Stable is not installed before updating.');
     $hook_updates = [
       'user' => '8000',
       'node' => '8003',
@@ -57,11 +59,14 @@ public function testDatabaseLoaded() {
       $this->assertEqual($existing_updates[$expected_update], 1, new FormattableMarkup("@expected_update exists in 'existing_updates' key and only appears once.", ['@expected_update' => $expected_update]));
     }
 
-    // @todo there are no updates to run.
-    // $this->runUpdates();
+    $this->runUpdates();
     $this->assertEqual(\Drupal::config('system.site')->get('name'), 'Site-Install');
     $this->drupalGet('<front>');
     $this->assertText('Site-Install');
+    $extensions = \Drupal::service('config.storage')->read('core.extension');
+    $this->assertTrue(isset($extensions['theme']['stable']), 'Stable is installed after updating.');
+    $blocks = \Drupal::entityManager()->getStorage('block')->loadByProperties(['theme' => 'stable']);
+    $this->assertTrue(empty($blocks), 'No blocks have been placed for Stable.');
   }
 
 }
diff --git a/core/modules/system/system.install b/core/modules/system/system.install
index 69044a1..c9e8175 100644
--- a/core/modules/system/system.install
+++ b/core/modules/system/system.install
@@ -1464,6 +1464,7 @@ function system_update_8005() {
         break;
 
       case 'classy':
+      case 'stable':
         // Don't place any blocks or trigger custom themes installed warning.
         break;
 
@@ -1541,6 +1542,7 @@ function system_update_8006() {
 
       case 'seven':
       case 'classy':
+      case 'stable':
         // Don't place any blocks or trigger custom themes installed warning.
         break;
       default:
@@ -1806,23 +1808,6 @@ function system_update_8011() {
 }
 
 /**
- * Install the Stable base theme if needed.
- */
-function system_update_8012() {
-  $theme_handler = \Drupal::service('theme_handler');
-  // Ensure we have fresh info.
-  $theme_handler->rebuildThemeData();
-  foreach ($theme_handler->listInfo() as $theme) {
-    // We first check that a base theme is set because if it's set to false then
-    // it's unset in \Drupal\Core\Extension\ThemeHandler::rebuildThemeData().
-    if (isset($theme->info['base theme']) && $theme->info['base theme'] == 'stable') {
-      $theme_handler->install(['stable']);
-      return;
-    }
-  }
-}
-
-/**
  * Enable automated cron module and move the config into it.
  */
 function system_update_8013() {
@@ -1847,3 +1832,31 @@ function system_update_8013() {
 /**
  * @} End of "addtogroup updates-8.0.0-beta".
  */
+
+/**
+ * @addtogroup updates-8.0.0-rc
+ * @{
+ */
+
+/**
+ * Install the Stable base theme if needed.
+ */
+function system_update_8014() {
+  $theme_handler = \Drupal::service('theme_handler');
+  if ($theme_handler->themeExists('stable')) {
+    return;
+  }
+  $theme_handler->refreshInfo();
+  foreach ($theme_handler->listInfo() as $theme) {
+    // We first check that a base theme is set because if it's set to false then
+    // it's unset in \Drupal\Core\Extension\ThemeHandler::rebuildThemeData().
+    if (isset($theme->info['base theme']) && $theme->info['base theme'] == 'stable') {
+      $theme_handler->install(['stable']);
+      return;
+    }
+  }
+}
+
+/**
+ * @} End of "addtogroup updates-8.0.0-rc".
+ */
diff --git a/core/modules/system/tests/themes/test_theme/test_theme.info.yml b/core/modules/system/tests/themes/test_theme/test_theme.info.yml
index 4c1568c..fca49c2 100644
--- a/core/modules/system/tests/themes/test_theme/test_theme.info.yml
+++ b/core/modules/system/tests/themes/test_theme/test_theme.info.yml
@@ -44,12 +44,12 @@ libraries-override:
   core/drupal.dropbutton:
     css:
       component:
-        misc/dropbutton/dropbutton.css: /themes/my_theme/css/dropbutton.css
+        /core/themes/stable/css/core/dropbutton/dropbutton.css: /themes/my_theme/css/dropbutton.css
   # Use stream wrappers.
   core/drupal.vertical-tabs:
     css:
       component:
-        misc/vertical-tabs.css: public://my_css/vertical-tabs.css
+        /core/themes/stable/css/core/vertical-tabs.css: public://my_css/vertical-tabs.css
   # Use a protocol-relative URI.
   core/jquery.ui:
     css:
diff --git a/core/modules/views/src/Tests/Plugin/StyleGridTest.php b/core/modules/views/src/Tests/Plugin/StyleGridTest.php
index 6dbac6b..698d2ba 100644
--- a/core/modules/views/src/Tests/Plugin/StyleGridTest.php
+++ b/core/modules/views/src/Tests/Plugin/StyleGridTest.php
@@ -53,7 +53,7 @@ public function testGrid() {
 
     // Ensure styles are properly added for grid views.
     $this->drupalGet('test-grid');
-    $this->assertRaw('views/css/views.module.css');
+    $this->assertRaw('stable/css/views/views.module.css');
   }
 
   /**
diff --git a/core/tests/Drupal/KernelTests/Core/Theme/StableTemplateOverrideTest.php b/core/tests/Drupal/KernelTests/Core/Theme/StableTemplateOverrideTest.php
new file mode 100644
index 0000000..69d9e8c
--- /dev/null
+++ b/core/tests/Drupal/KernelTests/Core/Theme/StableTemplateOverrideTest.php
@@ -0,0 +1,108 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\KernelTests\Core\Theme\StableTemplateOverrideTest.
+ */
+
+namespace Drupal\KernelTests\Core\Theme;
+
+use Drupal\Core\Theme\Registry;
+use Drupal\KernelTests\KernelTestBase;
+
+/**
+ * Tests Stable's template overrides.
+ *
+ * @group Theme
+ */
+class StableTemplateOverrideTest extends KernelTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public static $modules = ['system', 'user'];
+
+  /**
+   * An array of template names to skip, without the extension.
+   *
+   * @var string[]
+   */
+  protected $templatesToSkip = [
+    'views-form-views-form',
+  ];
+
+  /**
+   * The theme handler.
+   *
+   * @var \Drupal\Core\Extension\ThemeHandlerInterface
+   */
+  protected $themeHandler;
+
+  /**
+   * A list of all core modules.
+   *
+   * @var string[]
+   */
+  protected $allModules;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setUp() {
+    parent::setUp();
+    $this->themeHandler = $this->container->get('theme_handler');
+
+    $this->container->get('theme_installer')->install(['stable']);
+
+    $this->installSchema('system', 'router');
+    $this->installAllModules();
+  }
+
+  /**
+   * Installs all core modules.
+   */
+  protected function installAllModules() {
+    // Needed for system_rebuild_module_data().
+    include_once $this->root . '/core/modules/system/system.module';
+
+    // Enable all core modules.
+    $all_modules = system_rebuild_module_data();
+    $all_modules = array_filter($all_modules, function ($module) {
+      // Filter contrib, hidden, already enabled modules and modules in the
+      // Testing package.
+      if ($module->origin !== 'core' || !empty($module->info['hidden']) || $module->status == TRUE || $module->info['package'] == 'Testing') {
+        return FALSE;
+      }
+      return TRUE;
+    });
+    $this->allModules = array_keys($all_modules);
+    sort($this->allModules);
+
+    $module_installer = $this->container->get('module_installer');
+    $module_installer->install($this->allModules);
+
+    $this->installConfig(['system', 'user']);
+  }
+
+  /**
+   * Ensures that Stable overrides all relevant core templates.
+   */
+  public function testStableTemplateOverrides() {
+    $registry = new Registry(\Drupal::root(), \Drupal::cache(), \Drupal::lock(), \Drupal::moduleHandler(), $this->themeHandler, \Drupal::service('theme.initialization'), 'stable');
+    $registry->setThemeManager(\Drupal::theme());
+
+    $registry_full = $registry->get();
+
+    foreach ($registry_full as $hook => $info) {
+      if (isset($info['template'])) {
+        // Allow skipping templates.
+        if (in_array($info['template'], $this->templatesToSkip)) {
+          continue;
+        }
+
+        $this->assertEquals('core/themes/stable', $info['theme path'], $info['template'] . '.html.twig overridden in Stable.');
+      }
+    }
+  }
+
+}
diff --git a/core/themes/classy/classy.info.yml b/core/themes/classy/classy.info.yml
index 5ed9b80..007c566 100644
--- a/core/themes/classy/classy.info.yml
+++ b/core/themes/classy/classy.info.yml
@@ -4,7 +4,6 @@ description: 'A base theme with sensible default CSS classes added. Learn how to
 package: Core
 version: VERSION
 core: 8.x
-base theme: false
 hidden: true
 
 libraries:
diff --git a/core/themes/classy/templates/block/block--local-actions-block.html.twig b/core/themes/classy/templates/block/block--local-actions-block.html.twig
index 2a0f5c4..dbe2557 100644
--- a/core/themes/classy/templates/block/block--local-actions-block.html.twig
+++ b/core/themes/classy/templates/block/block--local-actions-block.html.twig
@@ -1,4 +1,4 @@
-{% extends "@block/block.html.twig" %}
+{% extends "@stable/block/block.html.twig" %}
 {#
 /**
  * @file
diff --git a/core/themes/classy/templates/block/block--local-tasks-block.html.twig b/core/themes/classy/templates/block/block--local-tasks-block.html.twig
index a191c60..ff960a5 100644
--- a/core/themes/classy/templates/block/block--local-tasks-block.html.twig
+++ b/core/themes/classy/templates/block/block--local-tasks-block.html.twig
@@ -1,4 +1,4 @@
-{% extends "@block/block.html.twig" %}
+{% extends "@stable/block/block.html.twig" %}
 {#
 /**
  * @file
diff --git a/core/modules/block/css/block.admin.css b/core/themes/stable/css/block/block.admin.css
similarity index 100%
copy from core/modules/block/css/block.admin.css
copy to core/themes/stable/css/block/block.admin.css
diff --git a/core/modules/ckeditor/css/ckeditor-iframe.css b/core/themes/stable/css/ckeditor/ckeditor-iframe.css
similarity index 100%
copy from core/modules/ckeditor/css/ckeditor-iframe.css
copy to core/themes/stable/css/ckeditor/ckeditor-iframe.css
diff --git a/core/modules/ckeditor/css/ckeditor.admin.css b/core/themes/stable/css/ckeditor/ckeditor.admin.css
similarity index 100%
copy from core/modules/ckeditor/css/ckeditor.admin.css
copy to core/themes/stable/css/ckeditor/ckeditor.admin.css
diff --git a/core/modules/ckeditor/css/ckeditor.css b/core/themes/stable/css/ckeditor/ckeditor.css
similarity index 100%
copy from core/modules/ckeditor/css/ckeditor.css
copy to core/themes/stable/css/ckeditor/ckeditor.css
diff --git a/core/modules/ckeditor/css/plugins/drupalimagecaption/ckeditor.drupalimagecaption.css b/core/themes/stable/css/ckeditor/plugins/drupalimagecaption/ckeditor.drupalimagecaption.css
similarity index 100%
copy from core/modules/ckeditor/css/plugins/drupalimagecaption/ckeditor.drupalimagecaption.css
copy to core/themes/stable/css/ckeditor/plugins/drupalimagecaption/ckeditor.drupalimagecaption.css
diff --git a/core/modules/color/css/color.admin.css b/core/themes/stable/css/color/color.admin.css
similarity index 93%
copy from core/modules/color/css/color.admin.css
copy to core/themes/stable/css/color/color.admin.css
index 376275e..29b6c00 100644
--- a/core/modules/color/css/color.admin.css
+++ b/core/themes/stable/css/color/color.admin.css
@@ -39,12 +39,12 @@
 .color-palette__hook.is-down,
 .color-palette__hook.is-up,
 .color-palette__hook.is-both {
-  background: url(../images/hook.png) no-repeat 100% 0; /* LTR */
+  background: url(../../images/color/hook.png) no-repeat 100% 0; /* LTR */
 }
 [dir="rtl"] .color-palette__hook.is-down,
 [dir="rtl"] .color-palette__hook.is-up,
 [dir="rtl"] .color-palette__hook.is-both {
-  background: url(../images/hook-rtl.png) no-repeat 0 0;
+  background: url(../../images/color/hook-rtl.png) no-repeat 0 0;
 }
 .color-palette__hook.is-up {
   background-position: 100% -27px; /* LTR */
@@ -67,7 +67,7 @@ button.color-palette__lock,
   float: left; /* LTR */
   width: 20px;
   height: 19px;
-  background: url(../images/lock.png) no-repeat 50% 0;
+  background: url(../../images/color/lock.png) no-repeat 50% 0;
   cursor: pointer;
   position: relative;
   top: -1.7em;
diff --git a/core/modules/config_translation/css/config_translation.admin.css b/core/themes/stable/css/config_translation/config_translation.admin.css
similarity index 100%
copy from core/modules/config_translation/css/config_translation.admin.css
copy to core/themes/stable/css/config_translation/config_translation.admin.css
diff --git a/core/modules/content_translation/css/content_translation.admin.css b/core/themes/stable/css/content_translation/content_translation.admin.css
similarity index 100%
copy from core/modules/content_translation/css/content_translation.admin.css
copy to core/themes/stable/css/content_translation/content_translation.admin.css
diff --git a/core/modules/contextual/css/contextual.icons.theme.css b/core/themes/stable/css/contextual/contextual.icons.theme.css
similarity index 65%
copy from core/modules/contextual/css/contextual.icons.theme.css
copy to core/themes/stable/css/contextual/contextual.icons.theme.css
index 7eb3f43..561e450 100644
--- a/core/modules/contextual/css/contextual.icons.theme.css
+++ b/core/themes/stable/css/contextual/contextual.icons.theme.css
@@ -7,18 +7,18 @@
  * Toolbar tab icon.
  */
 .toolbar-bar .toolbar-icon-edit:before {
-  background-image: url(../../../misc/icons/bebebe/pencil.svg);
+  background-image: url(../../images/core/icons/bebebe/pencil.svg);
 }
 .toolbar-bar .toolbar-icon-edit:active:before,
 .toolbar-bar .toolbar-icon-edit.is-active:before {
-  background-image: url(../../../misc/icons/ffffff/pencil.svg);
+  background-image: url(../../images/core/icons/ffffff/pencil.svg);
 }
 
 /**
  * Contextual trigger.
  */
 .contextual .trigger {
-  background-image: url(../../../misc/icons/bebebe/pencil.svg);
+  background-image: url(../../images/core/icons/bebebe/pencil.svg);
   background-position: center center;
   background-repeat: no-repeat;
   background-size: 16px 16px;
@@ -30,10 +30,10 @@
 }
 
 .contextual .trigger:hover {
-  background-image: url(../../../misc/icons/787878/pencil.svg);
+  background-image: url(../../images/core/icons/787878/pencil.svg);
 }
 
 .contextual .trigger:focus {
-  background-image: url(../../../misc/icons/5181c6/pencil.svg);
+  background-image: url(../../images/core/icons/5181c6/pencil.svg);
   outline: none;
 }
diff --git a/core/modules/contextual/css/contextual.module.css b/core/themes/stable/css/contextual/contextual.module.css
similarity index 100%
copy from core/modules/contextual/css/contextual.module.css
copy to core/themes/stable/css/contextual/contextual.module.css
diff --git a/core/modules/contextual/css/contextual.theme.css b/core/themes/stable/css/contextual/contextual.theme.css
similarity index 100%
copy from core/modules/contextual/css/contextual.theme.css
copy to core/themes/stable/css/contextual/contextual.theme.css
diff --git a/core/modules/contextual/css/contextual.toolbar.css b/core/themes/stable/css/contextual/contextual.toolbar.css
similarity index 100%
copy from core/modules/contextual/css/contextual.toolbar.css
copy to core/themes/stable/css/contextual/contextual.toolbar.css
diff --git a/core/misc/dropbutton/dropbutton.css b/core/themes/stable/css/core/dropbutton/dropbutton.css
similarity index 100%
copy from core/misc/dropbutton/dropbutton.css
copy to core/themes/stable/css/core/dropbutton/dropbutton.css
diff --git a/core/misc/print.css b/core/themes/stable/css/core/print.css
similarity index 100%
copy from core/misc/print.css
copy to core/themes/stable/css/core/print.css
diff --git a/core/misc/vertical-tabs.css b/core/themes/stable/css/core/vertical-tabs.css
similarity index 100%
copy from core/misc/vertical-tabs.css
copy to core/themes/stable/css/core/vertical-tabs.css
diff --git a/core/modules/dblog/css/dblog.module.css b/core/themes/stable/css/dblog/dblog.module.css
similarity index 86%
copy from core/modules/dblog/css/dblog.module.css
copy to core/themes/stable/css/dblog/dblog.module.css
index e844e14..ed531b7 100644
--- a/core/modules/dblog/css/dblog.module.css
+++ b/core/themes/stable/css/dblog/dblog.module.css
@@ -27,11 +27,11 @@
   width: 16px;
 }
 .admin-dblog .dblog-warning .icon {
-  background-image: url(../../../misc/icons/e29700/warning.svg);
+  background-image: url(../../images/core/icons/e29700/warning.svg);
 }
 .admin-dblog .dblog-error .icon,
 .admin-dblog .dblog-critical .icon,
 .admin-dblog .dblog-alert .icon,
 .admin-dblog .dblog-emergency .icon {
-  background-image: url(../../../misc/icons/e32700/error.svg);
+  background-image: url(../../images/core/icons/e32700/error.svg);
 }
diff --git a/core/modules/field_ui/css/field_ui.admin.css b/core/themes/stable/css/field_ui/field_ui.admin.css
similarity index 100%
copy from core/modules/field_ui/css/field_ui.admin.css
copy to core/themes/stable/css/field_ui/field_ui.admin.css
diff --git a/core/modules/file/css/file.admin.css b/core/themes/stable/css/file/file.admin.css
similarity index 100%
copy from core/modules/file/css/file.admin.css
copy to core/themes/stable/css/file/file.admin.css
diff --git a/core/modules/filter/css/filter.admin.css b/core/themes/stable/css/filter/filter.admin.css
similarity index 95%
copy from core/modules/filter/css/filter.admin.css
copy to core/themes/stable/css/filter/filter.admin.css
index b67a86a..a865411 100644
--- a/core/modules/filter/css/filter.admin.css
+++ b/core/themes/stable/css/filter/filter.admin.css
@@ -52,7 +52,7 @@
   display: block;
   width: 16px;
   height: 16px;
-  background: transparent url(../../../misc/help.png);
+  background: transparent url(../../images/core/help.png);
 }
 [dir="rtl"] .filter-help a:after {
   right: auto;
diff --git a/core/modules/filter/css/filter.caption.css b/core/themes/stable/css/filter/filter.caption.css
similarity index 100%
copy from core/modules/filter/css/filter.caption.css
copy to core/themes/stable/css/filter/filter.caption.css
diff --git a/core/modules/image/css/image.admin.css b/core/themes/stable/css/image/image.admin.css
similarity index 100%
copy from core/modules/image/css/image.admin.css
copy to core/themes/stable/css/image/image.admin.css
diff --git a/core/modules/language/css/language.admin.css b/core/themes/stable/css/language/language.admin.css
similarity index 100%
copy from core/modules/language/css/language.admin.css
copy to core/themes/stable/css/language/language.admin.css
diff --git a/core/modules/locale/css/locale.admin.css b/core/themes/stable/css/locale/locale.admin.css
similarity index 94%
copy from core/modules/locale/css/locale.admin.css
copy to core/themes/stable/css/locale/locale.admin.css
index aa83c8b..d55b429 100644
--- a/core/modules/locale/css/locale.admin.css
+++ b/core/themes/stable/css/locale/locale.admin.css
@@ -74,12 +74,12 @@
   vertical-align: top;
 }
 .locale-translation-update__wrapper {
-  background: transparent url(../../../misc/menu-collapsed.png) left .6em no-repeat;
+  background: transparent url(../../images/core/menu-collapsed.png) left .6em no-repeat;
   margin-left: -12px;
   padding-left: 12px;
 }
 .expanded .locale-translation-update__wrapper {
-  background: transparent url(../../../misc/menu-expanded.png) left .6em no-repeat;
+  background: transparent url(../../images/core/menu-expanded.png) left .6em no-repeat;
 }
 #locale-translation-status-form .description {
   cursor: pointer;
diff --git a/core/modules/menu_ui/css/menu_ui.admin.css b/core/themes/stable/css/menu_ui/menu_ui.admin.css
similarity index 100%
copy from core/modules/menu_ui/css/menu_ui.admin.css
copy to core/themes/stable/css/menu_ui/menu_ui.admin.css
diff --git a/core/modules/node/css/node.admin.css b/core/themes/stable/css/node/node.admin.css
similarity index 100%
copy from core/modules/node/css/node.admin.css
copy to core/themes/stable/css/node/node.admin.css
diff --git a/core/modules/node/css/node.module.css b/core/themes/stable/css/node/node.module.css
similarity index 100%
copy from core/modules/node/css/node.module.css
copy to core/themes/stable/css/node/node.module.css
diff --git a/core/modules/node/css/node.preview.css b/core/themes/stable/css/node/node.preview.css
similarity index 100%
copy from core/modules/node/css/node.preview.css
copy to core/themes/stable/css/node/node.preview.css
diff --git a/core/modules/quickedit/css/quickedit.icons.theme.css b/core/themes/stable/css/quickedit/quickedit.icons.theme.css
similarity index 82%
copy from core/modules/quickedit/css/quickedit.icons.theme.css
copy to core/themes/stable/css/quickedit/quickedit.icons.theme.css
index 7845416..856a78b 100644
--- a/core/modules/quickedit/css/quickedit.icons.theme.css
+++ b/core/themes/stable/css/quickedit/quickedit.icons.theme.css
@@ -56,19 +56,19 @@
  * Images.
  */
 .quickedit .icon-close:before {
-  background-image: url(../../../misc/icons/787878/ex.svg);
+  background-image: url(../../images/core/icons/787878/ex.svg);
   height: 12px;
   top: 10px;
 }
 .quickedit .icon-close:hover:before,
 .quickedit .icon-close:active:before {
-  background-image: url(../../../misc/icons/000000/ex.svg);
+  background-image: url(../../images/core/icons/000000/ex.svg);
 }
 .quickedit .icon-throbber:before {
-  background-image: url(../images/icon-throbber.gif);
+  background-image: url(../../images/quickedit/icon-throbber.gif);
 }
 .quickedit .icon-pencil:before {
-  background-image: url(../../../misc/icons/5181c6/pencil.svg);
+  background-image: url(../../images/core/icons/5181c6/pencil.svg);
   background-position: left center;
   background-size: 1.3em;
 }
diff --git a/core/modules/quickedit/css/quickedit.module.css b/core/themes/stable/css/quickedit/quickedit.module.css
similarity index 100%
copy from core/modules/quickedit/css/quickedit.module.css
copy to core/themes/stable/css/quickedit/quickedit.module.css
diff --git a/core/modules/quickedit/css/quickedit.theme.css b/core/themes/stable/css/quickedit/quickedit.theme.css
similarity index 100%
copy from core/modules/quickedit/css/quickedit.theme.css
copy to core/themes/stable/css/quickedit/quickedit.theme.css
diff --git a/core/modules/shortcut/css/shortcut.icons.theme.css b/core/themes/stable/css/shortcut/shortcut.icons.theme.css
similarity index 73%
copy from core/modules/shortcut/css/shortcut.icons.theme.css
copy to core/themes/stable/css/shortcut/shortcut.icons.theme.css
index 99812fd..c84a7cb 100644
--- a/core/modules/shortcut/css/shortcut.icons.theme.css
+++ b/core/themes/stable/css/shortcut/shortcut.icons.theme.css
@@ -7,25 +7,25 @@
  * Toolbar tab icon.
  */
 .toolbar-bar .toolbar-icon-shortcut:before {
-  background-image: url(../../../misc/icons/bebebe/star.svg);
+  background-image: url(../../images/core/icons/bebebe/star.svg);
 }
 .toolbar-bar .toolbar-icon-shortcut:active:before,
 .toolbar-bar .toolbar-icon-shortcut.is-active:before {
-  background-image: url(../../../misc/icons/ffffff/star.svg);
+  background-image: url(../../images/core/icons/ffffff/star.svg);
 }
 
 /**
  * Add/remove links.
  */
 .shortcut-action__icon {
-  background: transparent url(../images/favstar.svg) no-repeat left top;
+  background: transparent url(../../images/shortcut/favstar.svg) no-repeat left top;
   width: 20px;
   height: 20px;
   display: inline-block;
   vertical-align: -2px;
 }
 [dir="rtl"] .shortcut-action__icon {
-  background-image: url(../images/favstar-rtl.svg);
+  background-image: url(../../images/shortcut/favstar-rtl.svg);
 }
 .shortcut-action--add:hover .shortcut-action__icon,
 .shortcut-action--add:focus .shortcut-action__icon {
diff --git a/core/modules/shortcut/css/shortcut.theme.css b/core/themes/stable/css/shortcut/shortcut.theme.css
similarity index 100%
copy from core/modules/shortcut/css/shortcut.theme.css
copy to core/themes/stable/css/shortcut/shortcut.theme.css
diff --git a/core/modules/simpletest/css/simpletest.module.css b/core/themes/stable/css/simpletest/simpletest.module.css
similarity index 100%
copy from core/modules/simpletest/css/simpletest.module.css
copy to core/themes/stable/css/simpletest/simpletest.module.css
diff --git a/core/modules/system/css/components/ajax-progress.module.css b/core/themes/stable/css/system/components/ajax-progress.module.css
similarity index 84%
copy from core/modules/system/css/components/ajax-progress.module.css
copy to core/themes/stable/css/system/components/ajax-progress.module.css
index 136c2e1..f1caf3a 100644
--- a/core/modules/system/css/components/ajax-progress.module.css
+++ b/core/themes/stable/css/system/components/ajax-progress.module.css
@@ -11,7 +11,7 @@
   float: right;
 }
 .ajax-progress-throbber .throbber {
-  background: transparent url(../../../../misc/throbber-active.gif) no-repeat 0px center;
+  background: transparent url(../../../images/core/throbber-active.gif) no-repeat 0px center;
   display: inline;
   padding: 1px 5px 2px;
 }
@@ -34,7 +34,7 @@ tr .ajax-progress-throbber .throbber {
   top: 48.5%;
   z-index: 1000;
   background-color: #232323;
-  background-image: url(../../../../misc/loading-small.gif);
+  background-image: url(../../../images/core/loading-small.gif);
   background-position: center center;
   background-repeat: no-repeat;
   border-radius: 7px;
diff --git a/core/modules/system/css/components/align.module.css b/core/themes/stable/css/system/components/align.module.css
similarity index 100%
copy from core/modules/system/css/components/align.module.css
copy to core/themes/stable/css/system/components/align.module.css
diff --git a/core/modules/system/css/components/autocomplete-loading.module.css b/core/themes/stable/css/system/components/autocomplete-loading.module.css
similarity index 77%
copy from core/modules/system/css/components/autocomplete-loading.module.css
copy to core/themes/stable/css/system/components/autocomplete-loading.module.css
index 40d3323..48a9e9a 100644
--- a/core/modules/system/css/components/autocomplete-loading.module.css
+++ b/core/themes/stable/css/system/components/autocomplete-loading.module.css
@@ -6,7 +6,7 @@
  */
 
 .js input.form-autocomplete {
-  background-image: url(../../../../misc/throbber-inactive.png);
+  background-image: url(../../../images/core/throbber-inactive.png);
   background-position: 100% center; /* LTR */
   background-repeat: no-repeat;
 }
@@ -14,7 +14,7 @@
   background-position: 0% center;
 }
 .js input.form-autocomplete.ui-autocomplete-loading {
-  background-image: url(../../../../misc/throbber-active.gif);
+  background-image: url(../../../images/core/throbber-active.gif);
   background-position: 100% center; /* LTR */
 }
 .js[dir="rtl"] input.form-autocomplete.ui-autocomplete-loading {
diff --git a/core/modules/system/css/components/clearfix.module.css b/core/themes/stable/css/system/components/clearfix.module.css
similarity index 100%
copy from core/modules/system/css/components/clearfix.module.css
copy to core/themes/stable/css/system/components/clearfix.module.css
diff --git a/core/modules/system/css/components/container-inline.module.css b/core/themes/stable/css/system/components/container-inline.module.css
similarity index 100%
copy from core/modules/system/css/components/container-inline.module.css
copy to core/themes/stable/css/system/components/container-inline.module.css
diff --git a/core/modules/system/css/components/details.module.css b/core/themes/stable/css/system/components/details.module.css
similarity index 100%
copy from core/modules/system/css/components/details.module.css
copy to core/themes/stable/css/system/components/details.module.css
diff --git a/core/modules/system/css/components/fieldgroup.module.css b/core/themes/stable/css/system/components/fieldgroup.module.css
similarity index 100%
copy from core/modules/system/css/components/fieldgroup.module.css
copy to core/themes/stable/css/system/components/fieldgroup.module.css
diff --git a/core/modules/system/css/components/hidden.module.css b/core/themes/stable/css/system/components/hidden.module.css
similarity index 100%
copy from core/modules/system/css/components/hidden.module.css
copy to core/themes/stable/css/system/components/hidden.module.css
diff --git a/core/modules/system/css/components/item-list.module.css b/core/themes/stable/css/system/components/item-list.module.css
similarity index 100%
copy from core/modules/system/css/components/item-list.module.css
copy to core/themes/stable/css/system/components/item-list.module.css
diff --git a/core/modules/system/css/components/js.module.css b/core/themes/stable/css/system/components/js.module.css
similarity index 100%
copy from core/modules/system/css/components/js.module.css
copy to core/themes/stable/css/system/components/js.module.css
diff --git a/core/modules/system/css/components/nowrap.module.css b/core/themes/stable/css/system/components/nowrap.module.css
similarity index 100%
copy from core/modules/system/css/components/nowrap.module.css
copy to core/themes/stable/css/system/components/nowrap.module.css
diff --git a/core/modules/system/css/components/position-container.module.css b/core/themes/stable/css/system/components/position-container.module.css
similarity index 100%
copy from core/modules/system/css/components/position-container.module.css
copy to core/themes/stable/css/system/components/position-container.module.css
diff --git a/core/modules/system/css/components/progress.module.css b/core/themes/stable/css/system/components/progress.module.css
similarity index 100%
copy from core/modules/system/css/components/progress.module.css
copy to core/themes/stable/css/system/components/progress.module.css
diff --git a/core/modules/system/css/components/reset-appearance.module.css b/core/themes/stable/css/system/components/reset-appearance.module.css
similarity index 100%
copy from core/modules/system/css/components/reset-appearance.module.css
copy to core/themes/stable/css/system/components/reset-appearance.module.css
diff --git a/core/modules/system/css/components/resize.module.css b/core/themes/stable/css/system/components/resize.module.css
similarity index 100%
copy from core/modules/system/css/components/resize.module.css
copy to core/themes/stable/css/system/components/resize.module.css
diff --git a/core/modules/system/css/components/sticky-header.module.css b/core/themes/stable/css/system/components/sticky-header.module.css
similarity index 100%
copy from core/modules/system/css/components/sticky-header.module.css
copy to core/themes/stable/css/system/components/sticky-header.module.css
diff --git a/core/modules/system/css/components/tabledrag.module.css b/core/themes/stable/css/system/components/tabledrag.module.css
similarity index 91%
copy from core/modules/system/css/components/tabledrag.module.css
copy to core/themes/stable/css/system/components/tabledrag.module.css
index a4f0f20..687bdc2 100644
--- a/core/modules/system/css/components/tabledrag.module.css
+++ b/core/themes/stable/css/system/components/tabledrag.module.css
@@ -37,7 +37,7 @@ a.tabledrag-handle:hover {
   text-decoration: none;
 }
 a.tabledrag-handle .handle {
-  background: url(../../../../misc/icons/787878/move.svg) no-repeat 6px 7px;
+  background: url(../../../images/core/icons/787878/move.svg) no-repeat 6px 7px;
   height: 14px;
   margin: -0.4em 0.5em 0;
   padding: 0.42em 0.5em;
@@ -45,7 +45,7 @@ a.tabledrag-handle .handle {
 }
 a.tabledrag-handle:hover .handle,
 a.tabledrag-handle:focus .handle {
-  background-image: url(../../../../misc/icons/000000/move.svg);
+  background-image: url(../../../images/core/icons/000000/move.svg);
 }
 .touchevents .draggable td {
   padding: 0 10px;
diff --git a/core/modules/system/css/components/tablesort.module.css b/core/themes/stable/css/system/components/tablesort.module.css
similarity index 59%
copy from core/modules/system/css/components/tablesort.module.css
copy to core/themes/stable/css/system/components/tablesort.module.css
index 5e0e711..d3d34e6 100644
--- a/core/modules/system/css/components/tablesort.module.css
+++ b/core/themes/stable/css/system/components/tablesort.module.css
@@ -12,8 +12,8 @@
   background-size: 100%;
 }
 .tablesort--asc {
-  background-image: url(../../../../misc/icons/787878/twistie-down.svg);
+  background-image: url(../../../images/core/icons/787878/twistie-down.svg);
 }
 .tablesort--desc {
-  background-image: url(../../../../misc/icons/787878/twistie-up.svg);
+  background-image: url(../../../images/core/icons/787878/twistie-up.svg);
 }
diff --git a/core/themes/stable/css/system/components/tree-child.module.css b/core/themes/stable/css/system/components/tree-child.module.css
new file mode 100644
index 0000000..a09b389
--- /dev/null
+++ b/core/themes/stable/css/system/components/tree-child.module.css
@@ -0,0 +1,18 @@
+/**
+ * @file
+ * Visual styles for a nested tree child.
+ */
+
+div.tree-child {
+  background: url(../../../images/core/tree.png) no-repeat 11px center; /* LTR */
+}
+div.tree-child-last {
+  background: url(../../../images/core/tree-bottom.png) no-repeat 11px center; /* LTR */
+}
+[dir="rtl"] div.tree-child,
+[dir="rtl"] div.tree-child-last {
+  background-position: -65px center;
+}
+div.tree-child-horizontal {
+  background: url(../../../images/core/tree.png) no-repeat -11px center;
+}
diff --git a/core/modules/system/css/system.admin.css b/core/themes/stable/css/system/system.admin.css
similarity index 95%
copy from core/modules/system/css/system.admin.css
copy to core/themes/stable/css/system/system.admin.css
index 6bfd6f8..c8e20cf 100644
--- a/core/modules/system/css/system.admin.css
+++ b/core/themes/stable/css/system/system.admin.css
@@ -182,19 +182,19 @@ small .admin-link:after {
   float: right;
 }
 .module-link-help {
-  background: url(../../../misc/icons/787878/questionmark-disc.svg) 0 50% no-repeat; /* LTR */
+  background: url(../../images/core/icons/787878/questionmark-disc.svg) 0 50% no-repeat; /* LTR */
 }
 [dir="rtl"] .module-link-help {
   background-position: top 50% right 0;
 }
 .module-link-permissions {
-  background: url(../../../misc/icons/787878/key.svg) 0 50% no-repeat; /* LTR */
+  background: url(../../images/core/icons/787878/key.svg) 0 50% no-repeat; /* LTR */
 }
 [dir="rtl"] .module-link-permissions {
   background-position: top 50% right 0;
 }
 .module-link-configure {
-  background: url(../../../misc/icons/787878/cog.svg) 0 50% no-repeat; /* LTR */
+  background: url(../../images/core/icons/787878/cog.svg) 0 50% no-repeat; /* LTR */
 }
 [dir="rtl"] .module-link-configure {
   background-position: top 50% right 0;
@@ -227,10 +227,10 @@ small .admin-link:after {
   right: 12px;
 }
 .system-status-report__status-icon--error:before {
-  background-image: url(../../../misc/icons/e32700/error.svg);
+  background-image: url(../../images/core/icons/e32700/error.svg);
 }
 .system-status-report__status-icon--warning:before {
-  background-image: url(../../../misc/icons/e29700/warning.svg);
+  background-image: url(../../images/core/icons/e29700/warning.svg);
 }
 
 /**
diff --git a/core/modules/system/css/system.diff.css b/core/themes/stable/css/system/system.diff.css
similarity index 100%
copy from core/modules/system/css/system.diff.css
copy to core/themes/stable/css/system/system.diff.css
diff --git a/core/modules/system/css/system.maintenance.css b/core/themes/stable/css/system/system.maintenance.css
similarity index 100%
copy from core/modules/system/css/system.maintenance.css
copy to core/themes/stable/css/system/system.maintenance.css
diff --git a/core/modules/taxonomy/css/taxonomy.theme.css b/core/themes/stable/css/taxonomy/taxonomy.theme.css
similarity index 100%
copy from core/modules/taxonomy/css/taxonomy.theme.css
copy to core/themes/stable/css/taxonomy/taxonomy.theme.css
diff --git a/core/modules/toolbar/css/toolbar.icons.theme.css b/core/themes/stable/css/toolbar/toolbar.icons.theme.css
similarity index 74%
copy from core/modules/toolbar/css/toolbar.icons.theme.css
copy to core/themes/stable/css/toolbar/toolbar.icons.theme.css
index c52f868..54942d5 100644
--- a/core/modules/toolbar/css/toolbar.icons.theme.css
+++ b/core/themes/stable/css/toolbar/toolbar.icons.theme.css
@@ -72,78 +72,78 @@
  * Top level icons.
  */
 .toolbar-bar .toolbar-icon-menu:before {
-  background-image: url(../../../misc/icons/bebebe/hamburger.svg);
+  background-image: url(../../images/core/icons/bebebe/hamburger.svg);
 }
 .toolbar-bar .toolbar-icon-menu:active:before,
 .toolbar-bar .toolbar-icon-menu.is-active:before {
-  background-image: url(../../../misc/icons/ffffff/hamburger.svg);
+  background-image: url(../../images/core/icons/ffffff/hamburger.svg);
 }
 .toolbar-bar .toolbar-icon-help:before {
-  background-image: url(../../../misc/icons/bebebe/questionmark-disc.svg);
+  background-image: url(../../images/core/icons/bebebe/questionmark-disc.svg);
 }
 .toolbar-bar .toolbar-icon-help:active:before,
 .toolbar-bar .toolbar-icon-help.is-active:before {
-  background-image: url(../../../misc/icons/ffffff/questionmark-disc.svg);
+  background-image: url(../../images/core/icons/ffffff/questionmark-disc.svg);
 }
 
 /**
  * Main menu icons.
  */
 .toolbar-icon-system-admin-content:before {
-  background-image: url(../../../misc/icons/787878/file.svg);
+  background-image: url(../../images/core/icons/787878/file.svg);
 }
 .toolbar-icon-system-admin-content:active:before,
 .toolbar-icon-system-admin-content.is-active:before {
-  background-image: url(../../../misc/icons/000000/file.svg);
+  background-image: url(../../images/core/icons/000000/file.svg);
 }
 .toolbar-icon-system-admin-structure:before {
-  background-image: url(../../../misc/icons/787878/orgchart.svg);
+  background-image: url(../../images/core/icons/787878/orgchart.svg);
 }
 .toolbar-icon-system-admin-structure:active:before,
 .toolbar-icon-system-admin-structure.is-active:before {
-  background-image: url(../../../misc/icons/000000/orgchart.svg);
+  background-image: url(../../images/core/icons/000000/orgchart.svg);
 }
 .toolbar-icon-system-themes-page:before {
-  background-image: url(../../../misc/icons/787878/paintbrush.svg);
+  background-image: url(../../images/core/icons/787878/paintbrush.svg);
 }
 .toolbar-icon-system-themes-page:active:before,
 .toolbar-icon-system-themes-page.is-active:before {
-  background-image: url(../../../misc/icons/000000/paintbrush.svg);
+  background-image: url(../../images/core/icons/000000/paintbrush.svg);
 }
 .toolbar-icon-entity-user-collection:before {
-  background-image: url(../../../misc/icons/787878/people.svg);
+  background-image: url(../../images/core/icons/787878/people.svg);
 }
 .toolbar-icon-entity-user-collection:active:before,
 .toolbar-icon-entity-user-collection.is-active:before {
-  background-image: url(../../../misc/icons/000000/people.svg);
+  background-image: url(../../images/core/icons/000000/people.svg);
 }
 .toolbar-icon-system-modules-list:before {
-  background-image: url(../../../misc/icons/787878/puzzlepiece.svg);
+  background-image: url(../../images/core/icons/787878/puzzlepiece.svg);
 }
 .toolbar-icon-system-modules-list:active:before,
 .toolbar-icon-system-modules-list.is-active:before {
-  background-image: url(../../../misc/icons/000000/puzzlepiece.svg);
+  background-image: url(../../images/core/icons/000000/puzzlepiece.svg);
 }
 .toolbar-icon-system-admin-config:before {
-  background-image: url(../../../misc/icons/787878/wrench.svg);
+  background-image: url(../../images/core/icons/787878/wrench.svg);
 }
 .toolbar-icon-system-admin-config:active:before,
 .toolbar-icon-system-admin-config.is-active:before {
-  background-image: url(../../../misc/icons/000000/wrench.svg);
+  background-image: url(../../images/core/icons/000000/wrench.svg);
 }
 .toolbar-icon-system-admin-reports:before {
-  background-image: url(../../../misc/icons/787878/barchart.svg);
+  background-image: url(../../images/core/icons/787878/barchart.svg);
 }
 .toolbar-icon-system-admin-reports:active:before,
 .toolbar-icon-system-admin-reports.is-active:before {
-  background-image: url(../../../misc/icons/000000/barchart.svg);
+  background-image: url(../../images/core/icons/000000/barchart.svg);
 }
 .toolbar-icon-help-main:before {
-  background-image: url(../../../misc/icons/787878/questionmark-disc.svg);
+  background-image: url(../../images/core/icons/787878/questionmark-disc.svg);
 }
 .toolbar-icon-help-main:active:before,
 .toolbar-icon-help-main.is-active:before {
-  background-image: url(../../../misc/icons/000000/questionmark-disc.svg);
+  background-image: url(../../images/core/icons/000000/questionmark-disc.svg);
 }
 
 @media only screen and (min-width: 16.5em) {
@@ -235,24 +235,24 @@
   right: 1.6667em;
 }
 .toolbar .toolbar-icon.toolbar-handle:before {
-  background-image: url(../../../misc/icons/5181c6/chevron-disc-down.svg);
+  background-image: url(../../images/core/icons/5181c6/chevron-disc-down.svg);
 }
 .toolbar .toolbar-icon.toolbar-handle.open:before {
-  background-image: url(../../../misc/icons/787878/chevron-disc-up.svg);
+  background-image: url(../../images/core/icons/787878/chevron-disc-up.svg);
 }
 .toolbar .toolbar-menu .toolbar-menu .toolbar-icon.toolbar-handle:before {
-  background-image: url(../../../misc/icons/5181c6/twistie-down.svg);
+  background-image: url(../../images/core/icons/5181c6/twistie-down.svg);
   background-size: 75%;
 }
 .toolbar .toolbar-menu .toolbar-menu .toolbar-icon.toolbar-handle.open:before {
-  background-image: url(../../../misc/icons/787878/twistie-up.svg);
+  background-image: url(../../images/core/icons/787878/twistie-up.svg);
   background-size: 75%;
 }
 .toolbar .toolbar-icon-escape-admin:before {
-  background-image: url(../../../misc/icons/bebebe/chevron-disc-left.svg);
+  background-image: url(../../images/core/icons/bebebe/chevron-disc-left.svg);
 }
 [dir="rtl"] .toolbar .toolbar-icon-escape-admin:before {
-  background-image: url(../../../misc/icons/bebebe/chevron-disc-right.svg);
+  background-image: url(../../images/core/icons/bebebe/chevron-disc-right.svg);
 }
 /**
  * Orientation toggle.
@@ -277,24 +277,24 @@
  * specific targeting, setting and unsetting.
  */
 .toolbar .toolbar-toggle-orientation [value="vertical"]:before {
-  background-image: url(../../../misc/icons/bebebe/push-left.svg); /* LTR */
+  background-image: url(../../images/core/icons/bebebe/push-left.svg); /* LTR */
 }
 .toolbar .toolbar-toggle-orientation [value="vertical"]:hover:before,
 .toolbar .toolbar-toggle-orientation [value="vertical"]:focus:before
  {
-  background-image: url(../../../misc/icons/787878/push-left.svg); /* LTR */
+  background-image: url(../../images/core/icons/787878/push-left.svg); /* LTR */
 }
 [dir="rtl"] .toolbar .toolbar-toggle-orientation [value="vertical"]:before {
-  background-image: url(../../../misc/icons/bebebe/push-right.svg);
+  background-image: url(../../images/core/icons/bebebe/push-right.svg);
 }
 [dir="rtl"] .toolbar .toolbar-toggle-orientation [value="vertical"]:hover:before,
 [dir="rtl"] .toolbar .toolbar-toggle-orientation [value="vertical"]:focus:before {
-  background-image: url(../../../misc/icons/787878/push-right.svg);
+  background-image: url(../../images/core/icons/787878/push-right.svg);
 }
 .toolbar .toolbar-toggle-orientation [value="horizontal"]:before {
-  background-image: url(../../../misc/icons/bebebe/push-up.svg);
+  background-image: url(../../images/core/icons/bebebe/push-up.svg);
 }
 .toolbar .toolbar-toggle-orientation [value="horizontal"]:hover:before,
 .toolbar .toolbar-toggle-orientation [value="horizontal"]:focus:before {
-  background-image: url(../../../misc/icons/787878/push-up.svg);
+  background-image: url(../../images/core/icons/787878/push-up.svg);
 }
diff --git a/core/modules/toolbar/css/toolbar.menu.css b/core/themes/stable/css/toolbar/toolbar.menu.css
similarity index 100%
copy from core/modules/toolbar/css/toolbar.menu.css
copy to core/themes/stable/css/toolbar/toolbar.menu.css
diff --git a/core/modules/toolbar/css/toolbar.module.css b/core/themes/stable/css/toolbar/toolbar.module.css
similarity index 100%
copy from core/modules/toolbar/css/toolbar.module.css
copy to core/themes/stable/css/toolbar/toolbar.module.css
diff --git a/core/modules/toolbar/css/toolbar.theme.css b/core/themes/stable/css/toolbar/toolbar.theme.css
similarity index 100%
copy from core/modules/toolbar/css/toolbar.theme.css
copy to core/themes/stable/css/toolbar/toolbar.theme.css
diff --git a/core/modules/tour/css/tour.module.css b/core/themes/stable/css/tour/tour.module.css
similarity index 100%
copy from core/modules/tour/css/tour.module.css
copy to core/themes/stable/css/tour/tour.module.css
diff --git a/core/modules/update/css/update.admin.theme.css b/core/themes/stable/css/update/update.admin.theme.css
similarity index 100%
copy from core/modules/update/css/update.admin.theme.css
copy to core/themes/stable/css/update/update.admin.theme.css
diff --git a/core/modules/user/css/user.admin.css b/core/themes/stable/css/user/user.admin.css
similarity index 100%
copy from core/modules/user/css/user.admin.css
copy to core/themes/stable/css/user/user.admin.css
diff --git a/core/modules/user/css/user.icons.admin.css b/core/themes/stable/css/user/user.icons.admin.css
similarity index 62%
copy from core/modules/user/css/user.icons.admin.css
copy to core/themes/stable/css/user/user.icons.admin.css
index 66c2366..f854686 100644
--- a/core/modules/user/css/user.icons.admin.css
+++ b/core/themes/stable/css/user/user.icons.admin.css
@@ -7,9 +7,9 @@
  * Toolbar tab icon.
  */
 .toolbar-bar .toolbar-icon-user:before {
-  background-image: url(../../../misc/icons/bebebe/person.svg);
+  background-image: url(../../images/core/icons/bebebe/person.svg);
 }
 .toolbar-bar .toolbar-icon-user:active:before,
 .toolbar-bar .toolbar-icon-user.is-active:before {
-  background-image: url(../../../misc/icons/ffffff/person.svg);
+  background-image: url(../../images/core/icons/ffffff/person.svg);
 }
diff --git a/core/modules/user/css/user.module.css b/core/themes/stable/css/user/user.module.css
similarity index 100%
copy from core/modules/user/css/user.module.css
copy to core/themes/stable/css/user/user.module.css
diff --git a/core/modules/views/css/views.module.css b/core/themes/stable/css/views/views.module.css
similarity index 100%
copy from core/modules/views/css/views.module.css
copy to core/themes/stable/css/views/views.module.css
diff --git a/core/modules/views_ui/css/views_ui.admin.css b/core/themes/stable/css/views_ui/views_ui.admin.css
similarity index 100%
copy from core/modules/views_ui/css/views_ui.admin.css
copy to core/themes/stable/css/views_ui/views_ui.admin.css
diff --git a/core/modules/views_ui/css/views_ui.admin.theme.css b/core/themes/stable/css/views_ui/views_ui.admin.theme.css
similarity index 99%
copy from core/modules/views_ui/css/views_ui.admin.theme.css
copy to core/themes/stable/css/views_ui/views_ui.admin.theme.css
index 4ab55c4..3bf3290 100644
--- a/core/modules/views_ui/css/views_ui.admin.theme.css
+++ b/core/themes/stable/css/views_ui/views_ui.admin.theme.css
@@ -25,7 +25,7 @@
 .views-admin .icon,
 .views-admin .icon-text {
   background-attachment: scroll;
-  background-image: url(../images/sprites.png);
+  background-image: url(../../images/views_ui/sprites.png);
   background-position: left top; /* LTR */
   background-repeat: no-repeat;
 }
diff --git a/core/modules/views_ui/css/views_ui.contextual.css b/core/themes/stable/css/views_ui/views_ui.contextual.css
similarity index 100%
copy from core/modules/views_ui/css/views_ui.contextual.css
copy to core/themes/stable/css/views_ui/views_ui.contextual.css
diff --git a/core/modules/color/images/hook-rtl.png b/core/themes/stable/images/color/hook-rtl.png
similarity index 100%
copy from core/modules/color/images/hook-rtl.png
copy to core/themes/stable/images/color/hook-rtl.png
diff --git a/core/modules/color/images/hook.png b/core/themes/stable/images/color/hook.png
similarity index 100%
copy from core/modules/color/images/hook.png
copy to core/themes/stable/images/color/hook.png
diff --git a/core/modules/color/images/lock.png b/core/themes/stable/images/color/lock.png
similarity index 100%
copy from core/modules/color/images/lock.png
copy to core/themes/stable/images/color/lock.png
diff --git a/core/misc/druplicon.png b/core/themes/stable/images/core/druplicon.png
similarity index 100%
copy from core/misc/druplicon.png
copy to core/themes/stable/images/core/druplicon.png
diff --git a/core/misc/feed.svg b/core/themes/stable/images/core/feed.svg
similarity index 100%
copy from core/misc/feed.svg
copy to core/themes/stable/images/core/feed.svg
diff --git a/core/misc/help.png b/core/themes/stable/images/core/help.png
similarity index 100%
copy from core/misc/help.png
copy to core/themes/stable/images/core/help.png
diff --git a/core/misc/icons/000000/barchart.svg b/core/themes/stable/images/core/icons/000000/barchart.svg
similarity index 100%
copy from core/misc/icons/000000/barchart.svg
copy to core/themes/stable/images/core/icons/000000/barchart.svg
diff --git a/core/misc/icons/000000/chevron-left.svg b/core/themes/stable/images/core/icons/000000/chevron-left.svg
similarity index 100%
copy from core/misc/icons/000000/chevron-left.svg
copy to core/themes/stable/images/core/icons/000000/chevron-left.svg
diff --git a/core/misc/icons/000000/chevron-right.svg b/core/themes/stable/images/core/icons/000000/chevron-right.svg
similarity index 100%
copy from core/misc/icons/000000/chevron-right.svg
copy to core/themes/stable/images/core/icons/000000/chevron-right.svg
diff --git a/core/misc/icons/000000/ex.svg b/core/themes/stable/images/core/icons/000000/ex.svg
similarity index 100%
copy from core/misc/icons/000000/ex.svg
copy to core/themes/stable/images/core/icons/000000/ex.svg
diff --git a/core/misc/icons/000000/file.svg b/core/themes/stable/images/core/icons/000000/file.svg
similarity index 100%
copy from core/misc/icons/000000/file.svg
copy to core/themes/stable/images/core/icons/000000/file.svg
diff --git a/core/misc/icons/000000/move.svg b/core/themes/stable/images/core/icons/000000/move.svg
similarity index 100%
copy from core/misc/icons/000000/move.svg
copy to core/themes/stable/images/core/icons/000000/move.svg
diff --git a/core/misc/icons/000000/orgchart.svg b/core/themes/stable/images/core/icons/000000/orgchart.svg
similarity index 100%
copy from core/misc/icons/000000/orgchart.svg
copy to core/themes/stable/images/core/icons/000000/orgchart.svg
diff --git a/core/misc/icons/000000/paintbrush.svg b/core/themes/stable/images/core/icons/000000/paintbrush.svg
similarity index 100%
copy from core/misc/icons/000000/paintbrush.svg
copy to core/themes/stable/images/core/icons/000000/paintbrush.svg
diff --git a/core/misc/icons/000000/people.svg b/core/themes/stable/images/core/icons/000000/people.svg
similarity index 100%
copy from core/misc/icons/000000/people.svg
copy to core/themes/stable/images/core/icons/000000/people.svg
diff --git a/core/misc/icons/000000/puzzlepiece.svg b/core/themes/stable/images/core/icons/000000/puzzlepiece.svg
similarity index 100%
copy from core/misc/icons/000000/puzzlepiece.svg
copy to core/themes/stable/images/core/icons/000000/puzzlepiece.svg
diff --git a/core/misc/icons/000000/questionmark-disc.svg b/core/themes/stable/images/core/icons/000000/questionmark-disc.svg
similarity index 100%
copy from core/misc/icons/000000/questionmark-disc.svg
copy to core/themes/stable/images/core/icons/000000/questionmark-disc.svg
diff --git a/core/misc/icons/000000/wrench.svg b/core/themes/stable/images/core/icons/000000/wrench.svg
similarity index 100%
copy from core/misc/icons/000000/wrench.svg
copy to core/themes/stable/images/core/icons/000000/wrench.svg
diff --git a/core/misc/icons/004875/twistie-down.svg b/core/themes/stable/images/core/icons/004875/twistie-down.svg
similarity index 100%
copy from core/misc/icons/004875/twistie-down.svg
copy to core/themes/stable/images/core/icons/004875/twistie-down.svg
diff --git a/core/misc/icons/004875/twistie-up.svg b/core/themes/stable/images/core/icons/004875/twistie-up.svg
similarity index 100%
copy from core/misc/icons/004875/twistie-up.svg
copy to core/themes/stable/images/core/icons/004875/twistie-up.svg
diff --git a/core/misc/icons/0074bd/chevron-left.svg b/core/themes/stable/images/core/icons/0074bd/chevron-left.svg
similarity index 100%
copy from core/misc/icons/0074bd/chevron-left.svg
copy to core/themes/stable/images/core/icons/0074bd/chevron-left.svg
diff --git a/core/misc/icons/0074bd/chevron-right.svg b/core/themes/stable/images/core/icons/0074bd/chevron-right.svg
similarity index 100%
copy from core/misc/icons/0074bd/chevron-right.svg
copy to core/themes/stable/images/core/icons/0074bd/chevron-right.svg
diff --git a/core/misc/icons/008ee6/twistie-down.svg b/core/themes/stable/images/core/icons/008ee6/twistie-down.svg
similarity index 100%
copy from core/misc/icons/008ee6/twistie-down.svg
copy to core/themes/stable/images/core/icons/008ee6/twistie-down.svg
diff --git a/core/misc/icons/008ee6/twistie-up.svg b/core/themes/stable/images/core/icons/008ee6/twistie-up.svg
similarity index 100%
copy from core/misc/icons/008ee6/twistie-up.svg
copy to core/themes/stable/images/core/icons/008ee6/twistie-up.svg
diff --git a/core/misc/icons/333333/caret-down.svg b/core/themes/stable/images/core/icons/333333/caret-down.svg
similarity index 100%
copy from core/misc/icons/333333/caret-down.svg
copy to core/themes/stable/images/core/icons/333333/caret-down.svg
diff --git a/core/misc/icons/424242/loupe.svg b/core/themes/stable/images/core/icons/424242/loupe.svg
similarity index 100%
copy from core/misc/icons/424242/loupe.svg
copy to core/themes/stable/images/core/icons/424242/loupe.svg
diff --git a/core/misc/icons/505050/loupe.svg b/core/themes/stable/images/core/icons/505050/loupe.svg
similarity index 100%
copy from core/misc/icons/505050/loupe.svg
copy to core/themes/stable/images/core/icons/505050/loupe.svg
diff --git a/core/misc/icons/5181c6/chevron-disc-down.svg b/core/themes/stable/images/core/icons/5181c6/chevron-disc-down.svg
similarity index 100%
copy from core/misc/icons/5181c6/chevron-disc-down.svg
copy to core/themes/stable/images/core/icons/5181c6/chevron-disc-down.svg
diff --git a/core/misc/icons/5181c6/chevron-disc-up.svg b/core/themes/stable/images/core/icons/5181c6/chevron-disc-up.svg
similarity index 100%
copy from core/misc/icons/5181c6/chevron-disc-up.svg
copy to core/themes/stable/images/core/icons/5181c6/chevron-disc-up.svg
diff --git a/core/misc/icons/5181c6/pencil.svg b/core/themes/stable/images/core/icons/5181c6/pencil.svg
similarity index 100%
copy from core/misc/icons/5181c6/pencil.svg
copy to core/themes/stable/images/core/icons/5181c6/pencil.svg
diff --git a/core/misc/icons/5181c6/twistie-down.svg b/core/themes/stable/images/core/icons/5181c6/twistie-down.svg
similarity index 100%
copy from core/misc/icons/5181c6/twistie-down.svg
copy to core/themes/stable/images/core/icons/5181c6/twistie-down.svg
diff --git a/core/misc/icons/5181c6/twistie-up.svg b/core/themes/stable/images/core/icons/5181c6/twistie-up.svg
similarity index 100%
copy from core/misc/icons/5181c6/twistie-up.svg
copy to core/themes/stable/images/core/icons/5181c6/twistie-up.svg
diff --git a/core/misc/icons/73b355/check.svg b/core/themes/stable/images/core/icons/73b355/check.svg
similarity index 100%
copy from core/misc/icons/73b355/check.svg
copy to core/themes/stable/images/core/icons/73b355/check.svg
diff --git a/core/misc/icons/787878/barchart.svg b/core/themes/stable/images/core/icons/787878/barchart.svg
similarity index 100%
copy from core/misc/icons/787878/barchart.svg
copy to core/themes/stable/images/core/icons/787878/barchart.svg
diff --git a/core/misc/icons/787878/chevron-disc-down.svg b/core/themes/stable/images/core/icons/787878/chevron-disc-down.svg
similarity index 100%
copy from core/misc/icons/787878/chevron-disc-down.svg
copy to core/themes/stable/images/core/icons/787878/chevron-disc-down.svg
diff --git a/core/misc/icons/787878/chevron-disc-up.svg b/core/themes/stable/images/core/icons/787878/chevron-disc-up.svg
similarity index 100%
copy from core/misc/icons/787878/chevron-disc-up.svg
copy to core/themes/stable/images/core/icons/787878/chevron-disc-up.svg
diff --git a/core/misc/icons/787878/cog.svg b/core/themes/stable/images/core/icons/787878/cog.svg
similarity index 100%
copy from core/misc/icons/787878/cog.svg
copy to core/themes/stable/images/core/icons/787878/cog.svg
diff --git a/core/misc/icons/787878/ex.svg b/core/themes/stable/images/core/icons/787878/ex.svg
similarity index 100%
copy from core/misc/icons/787878/ex.svg
copy to core/themes/stable/images/core/icons/787878/ex.svg
diff --git a/core/misc/icons/787878/file.svg b/core/themes/stable/images/core/icons/787878/file.svg
similarity index 100%
copy from core/misc/icons/787878/file.svg
copy to core/themes/stable/images/core/icons/787878/file.svg
diff --git a/core/misc/icons/787878/key.svg b/core/themes/stable/images/core/icons/787878/key.svg
similarity index 100%
copy from core/misc/icons/787878/key.svg
copy to core/themes/stable/images/core/icons/787878/key.svg
diff --git a/core/misc/icons/787878/move.svg b/core/themes/stable/images/core/icons/787878/move.svg
similarity index 100%
copy from core/misc/icons/787878/move.svg
copy to core/themes/stable/images/core/icons/787878/move.svg
diff --git a/core/misc/icons/787878/orgchart.svg b/core/themes/stable/images/core/icons/787878/orgchart.svg
similarity index 100%
copy from core/misc/icons/787878/orgchart.svg
copy to core/themes/stable/images/core/icons/787878/orgchart.svg
diff --git a/core/misc/icons/787878/paintbrush.svg b/core/themes/stable/images/core/icons/787878/paintbrush.svg
similarity index 100%
copy from core/misc/icons/787878/paintbrush.svg
copy to core/themes/stable/images/core/icons/787878/paintbrush.svg
diff --git a/core/misc/icons/787878/pencil.svg b/core/themes/stable/images/core/icons/787878/pencil.svg
similarity index 100%
copy from core/misc/icons/787878/pencil.svg
copy to core/themes/stable/images/core/icons/787878/pencil.svg
diff --git a/core/misc/icons/787878/people.svg b/core/themes/stable/images/core/icons/787878/people.svg
similarity index 100%
copy from core/misc/icons/787878/people.svg
copy to core/themes/stable/images/core/icons/787878/people.svg
diff --git a/core/misc/icons/787878/push-left.svg b/core/themes/stable/images/core/icons/787878/push-left.svg
similarity index 100%
copy from core/misc/icons/787878/push-left.svg
copy to core/themes/stable/images/core/icons/787878/push-left.svg
diff --git a/core/misc/icons/787878/push-right.svg b/core/themes/stable/images/core/icons/787878/push-right.svg
similarity index 100%
copy from core/misc/icons/787878/push-right.svg
copy to core/themes/stable/images/core/icons/787878/push-right.svg
diff --git a/core/misc/icons/787878/push-up.svg b/core/themes/stable/images/core/icons/787878/push-up.svg
similarity index 100%
copy from core/misc/icons/787878/push-up.svg
copy to core/themes/stable/images/core/icons/787878/push-up.svg
diff --git a/core/misc/icons/787878/puzzlepiece.svg b/core/themes/stable/images/core/icons/787878/puzzlepiece.svg
similarity index 100%
copy from core/misc/icons/787878/puzzlepiece.svg
copy to core/themes/stable/images/core/icons/787878/puzzlepiece.svg
diff --git a/core/misc/icons/787878/questionmark-disc.svg b/core/themes/stable/images/core/icons/787878/questionmark-disc.svg
similarity index 100%
copy from core/misc/icons/787878/questionmark-disc.svg
copy to core/themes/stable/images/core/icons/787878/questionmark-disc.svg
diff --git a/core/misc/icons/787878/twistie-down.svg b/core/themes/stable/images/core/icons/787878/twistie-down.svg
similarity index 100%
copy from core/misc/icons/787878/twistie-down.svg
copy to core/themes/stable/images/core/icons/787878/twistie-down.svg
diff --git a/core/misc/icons/787878/twistie-up.svg b/core/themes/stable/images/core/icons/787878/twistie-up.svg
similarity index 100%
copy from core/misc/icons/787878/twistie-up.svg
copy to core/themes/stable/images/core/icons/787878/twistie-up.svg
diff --git a/core/misc/icons/787878/wrench.svg b/core/themes/stable/images/core/icons/787878/wrench.svg
similarity index 100%
copy from core/misc/icons/787878/wrench.svg
copy to core/themes/stable/images/core/icons/787878/wrench.svg
diff --git a/core/misc/icons/bebebe/chevron-disc-left.svg b/core/themes/stable/images/core/icons/bebebe/chevron-disc-left.svg
similarity index 100%
copy from core/misc/icons/bebebe/chevron-disc-left.svg
copy to core/themes/stable/images/core/icons/bebebe/chevron-disc-left.svg
diff --git a/core/misc/icons/bebebe/chevron-disc-right.svg b/core/themes/stable/images/core/icons/bebebe/chevron-disc-right.svg
similarity index 100%
copy from core/misc/icons/bebebe/chevron-disc-right.svg
copy to core/themes/stable/images/core/icons/bebebe/chevron-disc-right.svg
diff --git a/core/misc/icons/bebebe/cog.svg b/core/themes/stable/images/core/icons/bebebe/cog.svg
similarity index 100%
copy from core/misc/icons/bebebe/cog.svg
copy to core/themes/stable/images/core/icons/bebebe/cog.svg
diff --git a/core/misc/icons/bebebe/ex.svg b/core/themes/stable/images/core/icons/bebebe/ex.svg
similarity index 100%
copy from core/misc/icons/bebebe/ex.svg
copy to core/themes/stable/images/core/icons/bebebe/ex.svg
diff --git a/core/misc/icons/bebebe/hamburger.svg b/core/themes/stable/images/core/icons/bebebe/hamburger.svg
similarity index 100%
copy from core/misc/icons/bebebe/hamburger.svg
copy to core/themes/stable/images/core/icons/bebebe/hamburger.svg
diff --git a/core/misc/icons/bebebe/house.svg b/core/themes/stable/images/core/icons/bebebe/house.svg
similarity index 100%
copy from core/misc/icons/bebebe/house.svg
copy to core/themes/stable/images/core/icons/bebebe/house.svg
diff --git a/core/misc/icons/bebebe/key.svg b/core/themes/stable/images/core/icons/bebebe/key.svg
similarity index 100%
copy from core/misc/icons/bebebe/key.svg
copy to core/themes/stable/images/core/icons/bebebe/key.svg
diff --git a/core/misc/icons/bebebe/move.svg b/core/themes/stable/images/core/icons/bebebe/move.svg
similarity index 100%
copy from core/misc/icons/bebebe/move.svg
copy to core/themes/stable/images/core/icons/bebebe/move.svg
diff --git a/core/misc/icons/bebebe/pencil.svg b/core/themes/stable/images/core/icons/bebebe/pencil.svg
similarity index 100%
copy from core/misc/icons/bebebe/pencil.svg
copy to core/themes/stable/images/core/icons/bebebe/pencil.svg
diff --git a/core/misc/icons/bebebe/person.svg b/core/themes/stable/images/core/icons/bebebe/person.svg
similarity index 100%
copy from core/misc/icons/bebebe/person.svg
copy to core/themes/stable/images/core/icons/bebebe/person.svg
diff --git a/core/misc/icons/bebebe/push-left.svg b/core/themes/stable/images/core/icons/bebebe/push-left.svg
similarity index 100%
copy from core/misc/icons/bebebe/push-left.svg
copy to core/themes/stable/images/core/icons/bebebe/push-left.svg
diff --git a/core/misc/icons/bebebe/push-right.svg b/core/themes/stable/images/core/icons/bebebe/push-right.svg
similarity index 100%
copy from core/misc/icons/bebebe/push-right.svg
copy to core/themes/stable/images/core/icons/bebebe/push-right.svg
diff --git a/core/misc/icons/bebebe/push-up.svg b/core/themes/stable/images/core/icons/bebebe/push-up.svg
similarity index 100%
copy from core/misc/icons/bebebe/push-up.svg
copy to core/themes/stable/images/core/icons/bebebe/push-up.svg
diff --git a/core/misc/icons/bebebe/questionmark-disc.svg b/core/themes/stable/images/core/icons/bebebe/questionmark-disc.svg
similarity index 100%
copy from core/misc/icons/bebebe/questionmark-disc.svg
copy to core/themes/stable/images/core/icons/bebebe/questionmark-disc.svg
diff --git a/core/misc/icons/bebebe/star-empty.svg b/core/themes/stable/images/core/icons/bebebe/star-empty.svg
similarity index 100%
copy from core/misc/icons/bebebe/star-empty.svg
copy to core/themes/stable/images/core/icons/bebebe/star-empty.svg
diff --git a/core/misc/icons/bebebe/star.svg b/core/themes/stable/images/core/icons/bebebe/star.svg
similarity index 100%
copy from core/misc/icons/bebebe/star.svg
copy to core/themes/stable/images/core/icons/bebebe/star.svg
diff --git a/core/misc/icons/e29700/warning.svg b/core/themes/stable/images/core/icons/e29700/warning.svg
similarity index 100%
copy from core/misc/icons/e29700/warning.svg
copy to core/themes/stable/images/core/icons/e29700/warning.svg
diff --git a/core/misc/icons/e32700/error.svg b/core/themes/stable/images/core/icons/e32700/error.svg
similarity index 100%
copy from core/misc/icons/e32700/error.svg
copy to core/themes/stable/images/core/icons/e32700/error.svg
diff --git a/core/misc/icons/ee0000/required.svg b/core/themes/stable/images/core/icons/ee0000/required.svg
similarity index 100%
copy from core/misc/icons/ee0000/required.svg
copy to core/themes/stable/images/core/icons/ee0000/required.svg
diff --git a/core/misc/icons/ffffff/ex.svg b/core/themes/stable/images/core/icons/ffffff/ex.svg
similarity index 100%
copy from core/misc/icons/ffffff/ex.svg
copy to core/themes/stable/images/core/icons/ffffff/ex.svg
diff --git a/core/misc/icons/ffffff/hamburger.svg b/core/themes/stable/images/core/icons/ffffff/hamburger.svg
similarity index 100%
copy from core/misc/icons/ffffff/hamburger.svg
copy to core/themes/stable/images/core/icons/ffffff/hamburger.svg
diff --git a/core/misc/icons/ffffff/house.svg b/core/themes/stable/images/core/icons/ffffff/house.svg
similarity index 100%
copy from core/misc/icons/ffffff/house.svg
copy to core/themes/stable/images/core/icons/ffffff/house.svg
diff --git a/core/misc/icons/ffffff/pencil.svg b/core/themes/stable/images/core/icons/ffffff/pencil.svg
similarity index 100%
copy from core/misc/icons/ffffff/pencil.svg
copy to core/themes/stable/images/core/icons/ffffff/pencil.svg
diff --git a/core/misc/icons/ffffff/person.svg b/core/themes/stable/images/core/icons/ffffff/person.svg
similarity index 100%
copy from core/misc/icons/ffffff/person.svg
copy to core/themes/stable/images/core/icons/ffffff/person.svg
diff --git a/core/misc/icons/ffffff/questionmark-disc.svg b/core/themes/stable/images/core/icons/ffffff/questionmark-disc.svg
similarity index 100%
copy from core/misc/icons/ffffff/questionmark-disc.svg
copy to core/themes/stable/images/core/icons/ffffff/questionmark-disc.svg
diff --git a/core/misc/icons/ffffff/star-empty.svg b/core/themes/stable/images/core/icons/ffffff/star-empty.svg
similarity index 100%
copy from core/misc/icons/ffffff/star-empty.svg
copy to core/themes/stable/images/core/icons/ffffff/star-empty.svg
diff --git a/core/misc/icons/ffffff/star.svg b/core/themes/stable/images/core/icons/ffffff/star.svg
similarity index 100%
copy from core/misc/icons/ffffff/star.svg
copy to core/themes/stable/images/core/icons/ffffff/star.svg
diff --git a/core/misc/icons/ffffff/twistie-down.svg b/core/themes/stable/images/core/icons/ffffff/twistie-down.svg
similarity index 100%
copy from core/misc/icons/ffffff/twistie-down.svg
copy to core/themes/stable/images/core/icons/ffffff/twistie-down.svg
diff --git a/core/misc/icons/ffffff/twistie-up.svg b/core/themes/stable/images/core/icons/ffffff/twistie-up.svg
similarity index 100%
copy from core/misc/icons/ffffff/twistie-up.svg
copy to core/themes/stable/images/core/icons/ffffff/twistie-up.svg
diff --git a/core/misc/icons/license.md b/core/themes/stable/images/core/icons/license.md
similarity index 100%
copy from core/misc/icons/license.md
copy to core/themes/stable/images/core/icons/license.md
diff --git a/core/misc/loading-small.gif b/core/themes/stable/images/core/loading-small.gif
similarity index 100%
copy from core/misc/loading-small.gif
copy to core/themes/stable/images/core/loading-small.gif
diff --git a/core/modules/views_ui/images/loading.gif b/core/themes/stable/images/core/loading.gif
similarity index 100%
copy from core/modules/views_ui/images/loading.gif
copy to core/themes/stable/images/core/loading.gif
diff --git a/core/misc/menu-collapsed-rtl.png b/core/themes/stable/images/core/menu-collapsed-rtl.png
similarity index 100%
copy from core/misc/menu-collapsed-rtl.png
copy to core/themes/stable/images/core/menu-collapsed-rtl.png
diff --git a/core/misc/menu-collapsed.png b/core/themes/stable/images/core/menu-collapsed.png
similarity index 100%
copy from core/misc/menu-collapsed.png
copy to core/themes/stable/images/core/menu-collapsed.png
diff --git a/core/misc/menu-expanded.png b/core/themes/stable/images/core/menu-expanded.png
similarity index 100%
copy from core/misc/menu-expanded.png
copy to core/themes/stable/images/core/menu-expanded.png
diff --git a/core/misc/menu-leaf.png b/core/themes/stable/images/core/menu-leaf.png
similarity index 100%
copy from core/misc/menu-leaf.png
copy to core/themes/stable/images/core/menu-leaf.png
diff --git a/core/misc/throbber-active.gif b/core/themes/stable/images/core/throbber-active.gif
similarity index 100%
copy from core/misc/throbber-active.gif
copy to core/themes/stable/images/core/throbber-active.gif
diff --git a/core/misc/throbber-inactive.png b/core/themes/stable/images/core/throbber-inactive.png
similarity index 100%
copy from core/misc/throbber-inactive.png
copy to core/themes/stable/images/core/throbber-inactive.png
diff --git a/core/misc/tree-bottom.png b/core/themes/stable/images/core/tree-bottom.png
similarity index 100%
copy from core/misc/tree-bottom.png
copy to core/themes/stable/images/core/tree-bottom.png
diff --git a/core/misc/tree.png b/core/themes/stable/images/core/tree.png
similarity index 100%
copy from core/misc/tree.png
copy to core/themes/stable/images/core/tree.png
diff --git a/core/modules/quickedit/images/icon-throbber.gif b/core/themes/stable/images/quickedit/icon-throbber.gif
similarity index 100%
copy from core/modules/quickedit/images/icon-throbber.gif
copy to core/themes/stable/images/quickedit/icon-throbber.gif
diff --git a/core/modules/shortcut/images/favstar-rtl.svg b/core/themes/stable/images/shortcut/favstar-rtl.svg
similarity index 100%
copy from core/modules/shortcut/images/favstar-rtl.svg
copy to core/themes/stable/images/shortcut/favstar-rtl.svg
diff --git a/core/modules/shortcut/images/favstar.svg b/core/themes/stable/images/shortcut/favstar.svg
similarity index 100%
copy from core/modules/shortcut/images/favstar.svg
copy to core/themes/stable/images/shortcut/favstar.svg
diff --git a/core/modules/views_ui/images/sprites.png b/core/themes/stable/images/views_ui/sprites.png
similarity index 100%
copy from core/modules/views_ui/images/sprites.png
copy to core/themes/stable/images/views_ui/sprites.png
diff --git a/core/themes/stable/stable.info.yml b/core/themes/stable/stable.info.yml
index 960a683..6815218 100644
--- a/core/themes/stable/stable.info.yml
+++ b/core/themes/stable/stable.info.yml
@@ -1,8 +1,239 @@
 name: Stable
 type: theme
-description: A default base theme using Drupal 8.0.0's core markup, CSS, and JavaScript.
+description: A default base theme using Drupal 8.0.0's core markup and CSS.
 package: Core
 version: VERSION
 core: 8.x
 base theme: false
 hidden: true
+
+libraries-override:
+  block/drupal.block.admin:
+    css:
+      theme:
+        css/block.admin.css: css/block/block.admin.css
+
+  ckeditor/drupal.ckeditor:
+    css:
+      state:
+        css/ckeditor.css: css/ckeditor/ckeditor.css
+  ckeditor/drupal.ckeditor.plugins.drupalimagecaption:
+    css:
+      component:
+        css/plugins/drupalimagecaption/ckeditor.drupalimagecaption.css: css/ckeditor/plugins/drupalimagecaption/ckeditor.drupalimagecaption.css
+  ckeditor/drupal.ckeditor.admin:
+    css:
+      theme:
+        css/ckeditor.admin.css: css/ckeditor/ckeditor.admin.css
+
+  color/admin:
+    css:
+      theme:
+        css/color.admin.css: css/color/color.admin.css
+
+  config_translation/drupal.config_translation.admin:
+    css:
+      theme:
+        css/config_translation.admin.css: css/config_translation/config_translation.admin.css
+
+  content_translation/drupal.content_translation.admin:
+    css:
+      theme:
+        css/content_translation.admin.css: css/content_translation/content_translation.admin.css
+
+  contextual/drupal.contextual-links:
+    css:
+      component:
+        css/contextual.module.css: css/contextual/contextual.module.css
+      theme:
+        css/contextual.theme.css: css/contextual/contextual.theme.css
+        css/contextual.icons.theme.css: css/contextual/contextual.icons.theme.css
+  contextual/drupal.contextual-toolbar:
+    css:
+      component:
+        css/contextual.toolbar.css: css/contextual/contextual.toolbar.css
+
+  core/drupal.dropbutton:
+    css:
+      component:
+        misc/dropbutton/dropbutton.css: css/core/dropbutton/dropbutton.css
+  core/drupal.vertical-tabs:
+    css:
+      component:
+        misc/vertical-tabs.css: css/core/vertical-tabs.css
+
+  dblog/drupal.dblog:
+    css:
+      component:
+        css/dblog.module.css: css/dblog/dblog.module.css
+
+  field_ui/drupal.field_ui:
+    css:
+      theme:
+        css/field_ui.admin.css: css/field_ui/field_ui.admin.css
+
+  file/drupal.file:
+    css:
+      theme:
+        css/file.admin.css: css/file/file.admin.css
+
+  filter/caption:
+    css:
+      component:
+        css/filter.caption.css: css/filter/filter.caption.css
+  filter/drupal.filter.admin:
+    css:
+      theme:
+        css/filter.admin.css: css/filter/filter.admin.css
+  filter/drupal.filter:
+    css:
+      theme:
+        css/filter.admin.css: css/filter/filter.admin.css
+  filter/caption:
+    css:
+      component:
+        css/filter.caption.css: css/filter/filter.caption.css
+
+  image/admin:
+    css:
+      theme:
+        css/image.admin.css: css/image/image.admin.css
+
+  language/drupal.language.admin:
+    css:
+      theme:
+        css/language.admin.css: css/language/language.admin.css
+
+  locale/drupal.locale.admin:
+    css:
+      component:
+        css/locale.admin.css: css/locale/locale.admin.css
+
+  menu_ui/drupal.menu_ui.adminforms:
+    css:
+      theme:
+        css/menu_ui.admin.css: css/menu_ui/menu_ui.admin.css
+
+  node/drupal.node:
+    css:
+      layout:
+        css/node.module.css: css/node/node.module.css
+  node/drupal.node.preview:
+    css:
+      theme:
+        css/node.preview.css: css/node/node.preview.css
+  node/form:
+    css:
+      layout:
+        css/node.module.css: css/node/node.module.css
+  node/drupal.node.admin:
+    css:
+      theme:
+        css/node.admin.css: css/node/node.admin.css
+
+  quickedit/quickedit:
+    css:
+      component:
+        css/quickedit.module.css: css/quickedit/quickedit.module.css
+      theme:
+        css/quickedit.theme.css: css/quickedit/quickedit.theme.css
+        css/quickedit.icons.theme.css: css/quickedit/quickedit.icons.theme.css
+
+  shortcut/drupal.shortcut:
+    css:
+      theme:
+        css/shortcut.theme.css: css/shortcut/shortcut.theme.css
+        css/shortcut.icons.theme.css: css/shortcut/shortcut.icons.theme.css
+
+  simpletest/drupal.simpletest:
+    css:
+      component:
+        css/simpletest.module.css: css/simpletest/simpletest.module.css
+
+  system/base:
+    css:
+      component:
+        css/components/ajax-progress.module.css: css/system/components/ajax-progress.module.css
+        css/components/align.module.css: css/system/components/align.module.css
+        css/components/autocomplete-loading.module.css: css/system/components/autocomplete-loading.module.css
+        css/components/fieldgroup.module.css: css/system/components/fieldgroup.module.css
+        css/components/container-inline.module.css: css/system/components/container-inline.module.css
+        css/components/clearfix.module.css: css/system/components/clearfix.module.css
+        css/components/details.module.css: css/system/components/details.module.css
+        css/components/hidden.module.css: css/system/components/hidden.module.css
+        css/components/item-list.module.css: css/system/components/item-list.module.css
+        css/components/js.module.css: css/system/components/js.module.css
+        css/components/nowrap.module.css: css/system/components/nowrap.module.css
+        css/components/position-container.module.css: css/system/components/position-container.module.css
+        css/components/progress.module.css: css/system/components/progress.module.css
+        css/components/reset-appearance.module.css: css/system/components/reset-appearance.module.css
+        css/components/resize.module.css: css/system/components/resize.module.css
+        css/components/sticky-header.module.css: css/system/components/sticky-header.module.css
+        css/components/tabledrag.module.css: css/system/components/tabledrag.module.css
+        css/components/tablesort.module.css: css/system/components/tablesort.module.css
+        css/components/tree-child.module.css: css/system/components/tree-child.module.css
+  system/admin:
+    css:
+      theme:
+        css/system.admin.css: css/system/system.admin.css
+  system/maintenance:
+    css:
+      theme:
+        css/system.maintenance.css: css/system/system.maintenance.css
+  system/diff:
+    css:
+      component:
+        css/system.diff.css: css/system/system.diff.css
+
+  taxonomy/drupal.taxonomy:
+    css:
+      component:
+        css/taxonomy.theme.css: css/taxonomy/taxonomy.theme.css
+
+  toolbar/toolbar:
+    css:
+      component:
+        css/toolbar.module.css: css/toolbar/toolbar.module.css
+      theme:
+        css/toolbar.theme.css: css/toolbar/toolbar.theme.css
+        css/toolbar.icons.theme.css: css/toolbar/toolbar.icons.theme.css
+  toolbar/toolbar.menu:
+    css:
+      state:
+        css/toolbar.menu.css: css/toolbar/toolbar.menu.css
+
+  tour/tour-styling:
+    css:
+      component:
+        css/tour.module.css: css/tour/tour.module.css
+
+  update/drupal.update.admin:
+    css:
+      theme:
+        css/update.admin.theme.css: css/update/update.admin.theme.css
+
+  user/drupal.user:
+    css:
+      component:
+        css/user.module.css: css/user/user.module.css
+  user/drupal.user.admin:
+    css:
+      theme:
+        css/user.admin.css: css/user/user.admin.css
+  user/drupal.user.icons:
+    css:
+      theme:
+        css/user.icons.admin.css: css/user/user.icons.admin.css
+
+  views/views.module:
+    css:
+      component:
+        css/views.module.css: css/views/views.module.css
+
+  views_ui/admin.styling:
+    css:
+      component:
+        css/views_ui.admin.css: css/views_ui/views_ui.admin.css
+      theme:
+        css/views_ui.admin.theme.css: css/views_ui/views_ui.admin.theme.css
+        css/views_ui.contextual.css: css/views_ui/views_ui.contextual.css
diff --git a/core/modules/system/templates/admin-block-content.html.twig b/core/themes/stable/templates/admin/admin-block-content.html.twig
similarity index 89%
copy from core/modules/system/templates/admin-block-content.html.twig
copy to core/themes/stable/templates/admin/admin-block-content.html.twig
index f1c5f27..b59cc85 100644
--- a/core/modules/system/templates/admin-block-content.html.twig
+++ b/core/themes/stable/templates/admin/admin-block-content.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for the content of an administrative block.
+ * Theme override for the content of an administrative block.
  *
  * Available variables:
  * - content: A list containing information about the block. Each element
@@ -12,8 +12,6 @@
  * - compact: Boolean indicating whether compact mode is turned on or not.
  *
  * @see template_preprocess_admin_block_content()
- *
- * @ingroup themeable
  */
 #}
 {%
diff --git a/core/modules/system/templates/admin-block.html.twig b/core/themes/stable/templates/admin/admin-block.html.twig
similarity index 89%
copy from core/modules/system/templates/admin-block.html.twig
copy to core/themes/stable/templates/admin/admin-block.html.twig
index c3dab0e..9464d40 100644
--- a/core/modules/system/templates/admin-block.html.twig
+++ b/core/themes/stable/templates/admin/admin-block.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for an administrative block.
+ * Theme override for an administrative block.
  *
  * Available variables:
  * - block: An array of information about the block, including:
@@ -10,8 +10,6 @@
  *   - content: (optional) The content of the block.
  *   - description: (optional) A description of the block.
  *     (Description should only be output if content is not available).
- *
- * @ingroup themeable
  */
 #}
 <div class="panel">
diff --git a/core/modules/system/templates/admin-page.html.twig b/core/themes/stable/templates/admin/admin-page.html.twig
similarity index 86%
copy from core/modules/system/templates/admin-page.html.twig
copy to core/themes/stable/templates/admin/admin-page.html.twig
index a2483f1..106876f 100644
--- a/core/modules/system/templates/admin-page.html.twig
+++ b/core/themes/stable/templates/admin/admin-page.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for an administrative page.
+ * Theme override for an administrative page.
  *
  * Available variables:
  * - system_compact_link: Themed link to toggle compact view.
@@ -10,8 +10,6 @@
  *   - blocks: A list of blocks within a container.
  *
  * @see template_preprocess_admin_page()
- *
- * @ingroup themeable
  */
 #}
 
diff --git a/core/modules/system/templates/authorize-report.html.twig b/core/themes/stable/templates/admin/authorize-report.html.twig
similarity index 81%
copy from core/modules/system/templates/authorize-report.html.twig
copy to core/themes/stable/templates/admin/authorize-report.html.twig
index 9144586..2e5a59c 100644
--- a/core/modules/system/templates/authorize-report.html.twig
+++ b/core/themes/stable/templates/admin/authorize-report.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for authorize.php operation report templates.
+ * Theme override for authorize.php operation report templates.
  *
  * This report displays the results of an operation run via authorize.php.
  *
@@ -10,8 +10,6 @@
  * - attributes: HTML attributes for the element.
  *
  * @see template_preprocess_authorize_report()
- *
- * @ingroup themeable
  */
 #}
 {% if messages %}
diff --git a/core/modules/block_content/templates/block-content-add-list.html.twig b/core/themes/stable/templates/admin/block-content-add-list.html.twig
similarity index 83%
copy from core/modules/block_content/templates/block-content-add-list.html.twig
copy to core/themes/stable/templates/admin/block-content-add-list.html.twig
index 0810461..ae99d1f 100644
--- a/core/modules/block_content/templates/block-content-add-list.html.twig
+++ b/core/themes/stable/templates/admin/block-content-add-list.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation to present a list of custom block types.
+ * Theme override to present a list of custom block types.
  *
  * Available variables:
  * - types: A collection of all the available custom block types.
@@ -10,8 +10,6 @@
  *   - description: A description of this custom block type.
  *
  * @see template_preprocess_block_content_add_list()
- *
- * @ingroup themeable
  */
 #}
 {% spaceless %}
diff --git a/core/modules/block/templates/block-list.html.twig b/core/themes/stable/templates/admin/block-list.html.twig
similarity index 95%
copy from core/modules/block/templates/block-list.html.twig
copy to core/themes/stable/templates/admin/block-list.html.twig
index 854d3ce..0da7e94 100644
--- a/core/modules/block/templates/block-list.html.twig
+++ b/core/themes/stable/templates/admin/block-list.html.twig
@@ -9,8 +9,6 @@
  *
  * Available variables:
  * - form: The block add/edit form.
- *
- * @ingroup themeable
  */
 #}
 <div class="layout-block-list clearfix">
diff --git a/core/modules/ckeditor/templates/ckeditor-settings-toolbar.html.twig b/core/themes/stable/templates/admin/ckeditor-settings-toolbar.html.twig
similarity index 97%
copy from core/modules/ckeditor/templates/ckeditor-settings-toolbar.html.twig
copy to core/themes/stable/templates/admin/ckeditor-settings-toolbar.html.twig
index bc8e836..392c494 100644
--- a/core/modules/ckeditor/templates/ckeditor-settings-toolbar.html.twig
+++ b/core/themes/stable/templates/admin/ckeditor-settings-toolbar.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for the CKEditor settings toolbar.
+ * Theme override for the CKEditor settings toolbar.
  *
  * Available variables:
  * - multiple_buttons: A list of buttons that may be added multiple times.
@@ -9,8 +9,6 @@
  * - active_buttons: A list of active button rows.
  *
  * @see template_preprocess_ckeditor_settings_toolbar()
- *
- * @ingroup themeable
  */
 #}
 {% spaceless %}
diff --git a/core/modules/color/templates/color-scheme-form.html.twig b/core/themes/stable/templates/admin/color-scheme-form.html.twig
similarity index 89%
copy from core/modules/color/templates/color-scheme-form.html.twig
copy to core/themes/stable/templates/admin/color-scheme-form.html.twig
index 3c6fdd0..c7328af 100644
--- a/core/modules/color/templates/color-scheme-form.html.twig
+++ b/core/themes/stable/templates/admin/color-scheme-form.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a theme's color form.
+ * Theme override for a theme's color form.
  *
  * Available variables:
  * - form: Form elements for the color scheme form, including:
@@ -11,8 +11,6 @@
  * - html_preview: A HTML preview of the theme's current color scheme.
  *
  * @see template_preprocess_color_scheme_form()
- *
- * @ingroup themeable
  */
 #}
 <div class="color-form clearfix">
diff --git a/core/modules/config_translation/templates/config_translation_manage_form_element.html.twig b/core/themes/stable/templates/admin/config_translation_manage_form_element.html.twig
similarity index 85%
copy from core/modules/config_translation/templates/config_translation_manage_form_element.html.twig
copy to core/themes/stable/templates/admin/config_translation_manage_form_element.html.twig
index 777514f..b476955 100644
--- a/core/modules/config_translation/templates/config_translation_manage_form_element.html.twig
+++ b/core/themes/stable/templates/admin/config_translation_manage_form_element.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a form element in config_translation.
+ * Theme override for a form element in config_translation.
  *
  * Available variables:
  * - element: Array that represents the element shown in the form.
@@ -10,8 +10,6 @@
  *
  * @see template_preprocess()
  * @see template_preprocess_config_translation_manage_form_element()
- *
- * @ingroup themeable
  */
 #}
 <div class="translation-set clearfix">
diff --git a/core/modules/field_ui/templates/field-ui-table.html.twig b/core/themes/stable/templates/admin/field-ui-table.html.twig
similarity index 96%
copy from core/modules/field_ui/templates/field-ui-table.html.twig
copy to core/themes/stable/templates/admin/field-ui-table.html.twig
index f7ff026..5a05852 100644
--- a/core/modules/field_ui/templates/field-ui-table.html.twig
+++ b/core/themes/stable/templates/admin/field-ui-table.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation to display a Field UI table.
+ * Theme override to display a Field UI table.
  *
  * Available variables:
  * - attributes: HTML attributes to apply to the <table> tag.
@@ -37,8 +37,6 @@
  * - header_columns: The number of columns in the header.
  *
  * @see template_preprocess_field_ui_table()
- *
- * @ingroup themeable
  */
 #}
 {# Add Ajax wrapper. #}
diff --git a/core/modules/image/templates/image-anchor.html.twig b/core/themes/stable/templates/admin/image-anchor.html.twig
similarity index 59%
copy from core/modules/image/templates/image-anchor.html.twig
copy to core/themes/stable/templates/admin/image-anchor.html.twig
index eb670a4..1d709dd 100644
--- a/core/modules/image/templates/image-anchor.html.twig
+++ b/core/themes/stable/templates/admin/image-anchor.html.twig
@@ -1,14 +1,12 @@
 {#
 /**
  * @file
- * Default theme implementation for a 3x3 grid of checkboxes for image anchors.
+ * Theme override for a 3x3 grid of checkboxes for image anchors.
  *
  * Available variables:
  * - table: HTML for the table of image anchors.
  *
  * @see template_preprocess_image_anchor()
- *
- * @ingroup themeable
  */
 #}
 {{ table }}
diff --git a/core/modules/image/templates/image-crop-summary.html.twig b/core/themes/stable/templates/admin/image-crop-summary.html.twig
similarity index 89%
copy from core/modules/image/templates/image-crop-summary.html.twig
copy to core/themes/stable/templates/admin/image-crop-summary.html.twig
index fc991b6..6f3b0fc 100644
--- a/core/modules/image/templates/image-crop-summary.html.twig
+++ b/core/themes/stable/templates/admin/image-crop-summary.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a summary of an image crop effect.
+ * Theme override for a summary of an image crop effect.
  *
  * Available variables:
  * - data: The current configuration for this resize effect, including:
@@ -13,8 +13,6 @@
  *   - id: The effect identifier.
  *   - label: The effect name.
  *   - description: The effect description.
- *
- * @ingroup themeable
  */
 #}
 {% if data.width and data.height -%}
diff --git a/core/modules/image/templates/image-resize-summary.html.twig b/core/themes/stable/templates/admin/image-resize-summary.html.twig
similarity index 87%
copy from core/modules/image/templates/image-resize-summary.html.twig
copy to core/themes/stable/templates/admin/image-resize-summary.html.twig
index f4084ef..fde09d2 100644
--- a/core/modules/image/templates/image-resize-summary.html.twig
+++ b/core/themes/stable/templates/admin/image-resize-summary.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a summary of an image resize effect.
+ * Theme override for a summary of an image resize effect.
  *
  * Available variables:
  * - data: The current configuration for this resize effect, including:
@@ -11,8 +11,6 @@
  *   - id: The effect identifier.
  *   - label: The effect name.
  *   - description: The effect description.
- *
- * @ingroup themeable
  */
 #}
 {% if data.width and data.height -%}
diff --git a/core/modules/image/templates/image-rotate-summary.html.twig b/core/themes/stable/templates/admin/image-rotate-summary.html.twig
similarity index 88%
copy from core/modules/image/templates/image-rotate-summary.html.twig
copy to core/themes/stable/templates/admin/image-rotate-summary.html.twig
index 705a0eb..542f2df 100644
--- a/core/modules/image/templates/image-rotate-summary.html.twig
+++ b/core/themes/stable/templates/admin/image-rotate-summary.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a summary of an image rotate effect.
+ * Theme override for a summary of an image rotate effect.
  *
  * Available variables:
  * - data: The current configuration for this resize effect, including:
@@ -14,8 +14,6 @@
  *   - id: The effect identifier.
  *   - label: The effect name.
  *   - description: The effect description.
- *
- * @ingroup themeable
  */
 #}
 {% if data.random %}
diff --git a/core/modules/image/templates/image-scale-summary.html.twig b/core/themes/stable/templates/admin/image-scale-summary.html.twig
similarity index 89%
copy from core/modules/image/templates/image-scale-summary.html.twig
copy to core/themes/stable/templates/admin/image-scale-summary.html.twig
index 32d75cc..bf54445 100644
--- a/core/modules/image/templates/image-scale-summary.html.twig
+++ b/core/themes/stable/templates/admin/image-scale-summary.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a summary of an image scale effect.
+ * Theme override for a summary of an image scale effect.
  *
  * Available variables:
  * - data: The current configuration for this resize effect, including:
@@ -12,8 +12,6 @@
  *   - id: The effect identifier.
  *   - label: The effect name.
  *   - description: The effect description.
- *
- * @ingroup themeable
  */
 #}
 {% if data.width and data.height -%}
diff --git a/core/modules/image/templates/image-style-preview.html.twig b/core/themes/stable/templates/admin/image-style-preview.html.twig
similarity index 96%
copy from core/modules/image/templates/image-style-preview.html.twig
copy to core/themes/stable/templates/admin/image-style-preview.html.twig
index d6e715c..3517b2c 100644
--- a/core/modules/image/templates/image-style-preview.html.twig
+++ b/core/themes/stable/templates/admin/image-style-preview.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation to display a preview of an image style.
+ * Theme override to display a preview of an image style.
  *
  * Available variables:
  * - style_id: The ID of the image style.
@@ -26,8 +26,6 @@
  *     - height: The height in pixels of the derivative image in the preview.
  *
  * @see template_preprocess_image_style_preview()
- *
- * @ingroup themeable
  */
 #}
 <div class="image-style-preview preview clearfix">
diff --git a/core/modules/system/templates/indentation.html.twig b/core/themes/stable/templates/admin/indentation.html.twig
similarity index 75%
copy from core/modules/system/templates/indentation.html.twig
copy to core/themes/stable/templates/admin/indentation.html.twig
index c7067fb..c8244b5 100644
--- a/core/modules/system/templates/indentation.html.twig
+++ b/core/themes/stable/templates/admin/indentation.html.twig
@@ -1,14 +1,12 @@
 {#
 /**
  * @file
- * Default theme implementation for a set of indentation divs.
+ * Theme override for a set of indentation divs.
  *
  * These <div> tags are used for drag and drop tables.
  *
  * Available variables:
  * - size: Optional. The number of indentations to create.
- *
- * @ingroup themeable
  */
 #}
 {% for i in 1..size if size > 0 %}<div class="js-indentation indentation">&nbsp;</div>{% endfor %}
diff --git a/core/modules/language/templates/language-content-settings-table.html.twig b/core/themes/stable/templates/admin/language-content-settings-table.html.twig
similarity index 69%
copy from core/modules/language/templates/language-content-settings-table.html.twig
copy to core/themes/stable/templates/admin/language-content-settings-table.html.twig
index ff2cdbd..5a8ba8c 100644
--- a/core/modules/language/templates/language-content-settings-table.html.twig
+++ b/core/themes/stable/templates/admin/language-content-settings-table.html.twig
@@ -1,15 +1,13 @@
 {#
 /**
  * @file
- * Default theme implementation to display a language content settings table.
+ * Theme override to display a language content settings table.
  *
  * Available variables:
  * - title: The title of the table.
  * - build: Table of content language settings.
  *
  * @see template_preprocess_language_content_settings_table()
- *
- * @ingroup themeable
  */
 #}
 <h4>{{ title }}</h4>
diff --git a/core/modules/language/templates/language-negotiation-configure-form.html.twig b/core/themes/stable/templates/admin/language-negotiation-configure-form.html.twig
similarity index 92%
copy from core/modules/language/templates/language-negotiation-configure-form.html.twig
copy to core/themes/stable/templates/admin/language-negotiation-configure-form.html.twig
index 12528ac..5029a65 100644
--- a/core/modules/language/templates/language-negotiation-configure-form.html.twig
+++ b/core/themes/stable/templates/admin/language-negotiation-configure-form.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
 * @file
-* Default theme implementation for a language negotiation configuration form.
+* Theme override for a language negotiation configuration form.
 *
 * Available variables:
 * - language_types: A list of language negotiation types. Each language type
@@ -16,8 +16,6 @@
 * - children: Remaining form items for all groups.
 *
 * @see template_preprocess_language_negotiation_configure_form()
-*
-* @ingroup themeable
 */
 #}
 {% for language_type in language_types %}
diff --git a/core/modules/locale/templates/locale-translation-last-check.html.twig b/core/themes/stable/templates/admin/locale-translation-last-check.html.twig
similarity index 84%
copy from core/modules/locale/templates/locale-translation-last-check.html.twig
copy to core/themes/stable/templates/admin/locale-translation-last-check.html.twig
index a54574b..1c5ebd0 100644
--- a/core/modules/locale/templates/locale-translation-last-check.html.twig
+++ b/core/themes/stable/templates/admin/locale-translation-last-check.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for the last time we checked for update data.
+ * Theme override for the last time we checked for update data.
  *
  * Available variables:
  * - last_checked: Whether or not locale updates have been checked before.
@@ -10,8 +10,6 @@
  * - link: A link to manually check available updates.
  *
  * @see template_preprocess_locale_translation_last_check()
- *
- * @ingroup themeable
  */
 #}
 <div class="locale checked">
diff --git a/core/modules/locale/templates/locale-translation-update-info.html.twig b/core/themes/stable/templates/admin/locale-translation-update-info.html.twig
similarity index 94%
copy from core/modules/locale/templates/locale-translation-update-info.html.twig
copy to core/themes/stable/templates/admin/locale-translation-update-info.html.twig
index 74cbffc..8e2bede 100644
--- a/core/modules/locale/templates/locale-translation-update-info.html.twig
+++ b/core/themes/stable/templates/admin/locale-translation-update-info.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for displaying translation status information.
+ * Theme override for displaying translation status information.
  *
  * Displays translation status information per language.
  *
@@ -11,8 +11,6 @@
  * - not_found: A list of modules missing translation updates.
  *
  * @see template_preprocess_locale_translation_update_info()
- *
- * @ingroup themeable
  */
 #}
 <div class="locale-translation-update__wrapper" tabindex="0" role="button">
diff --git a/core/modules/system/templates/maintenance-task-list.html.twig b/core/themes/stable/templates/admin/maintenance-task-list.html.twig
similarity index 86%
copy from core/modules/system/templates/maintenance-task-list.html.twig
copy to core/themes/stable/templates/admin/maintenance-task-list.html.twig
index 8b120a4..0fbeff9 100644
--- a/core/modules/system/templates/maintenance-task-list.html.twig
+++ b/core/themes/stable/templates/admin/maintenance-task-list.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a list of maintenance tasks to perform.
+ * Theme override for a list of maintenance tasks to perform.
  *
  * Available variables:
  * - tasks: A list of maintenance tasks to perform. Each item in the list has
@@ -10,8 +10,6 @@
  *   - attributes: HTML attributes for the maintenance task.
  *   - status: (optional) Text describing the status of the maintenance task,
  *     'active' or 'done'.
- *
- * @ingroup themeable
  */
 #}
 <h2 class="visually-hidden">{{ 'Installation tasks'|t }}</h2>
diff --git a/core/modules/simpletest/templates/simpletest-result-summary.html.twig b/core/themes/stable/templates/admin/simpletest-result-summary.html.twig
similarity index 86%
copy from core/modules/simpletest/templates/simpletest-result-summary.html.twig
copy to core/themes/stable/templates/admin/simpletest-result-summary.html.twig
index 2f87ed0..5523325 100644
--- a/core/modules/simpletest/templates/simpletest-result-summary.html.twig
+++ b/core/themes/stable/templates/admin/simpletest-result-summary.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for simpletest result summaries.
+ * Theme override for simpletest result summaries.
  *
  * Available variables:
  * - label: An optional label to be rendered before the results.
@@ -13,8 +13,6 @@
  * - debug: The number of debug messages.
  *
  * @see template_preprocess_simpletest_result_summary()
- *
- * @ingroup themeable
  */
 #}
 <div class="simpletest-{{ fail + exception == 0 ? 'pass' : 'fail' }}">
diff --git a/core/modules/system/templates/status-report.html.twig b/core/themes/stable/templates/admin/status-report.html.twig
similarity index 94%
copy from core/modules/system/templates/status-report.html.twig
copy to core/themes/stable/templates/admin/status-report.html.twig
index b6ad739..7f4c600 100644
--- a/core/modules/system/templates/status-report.html.twig
+++ b/core/themes/stable/templates/admin/status-report.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for the status report.
+ * Theme override for the status report.
  *
  * Available variables:
  * - requirements: Contains multiple requirement instances.
@@ -13,8 +13,6 @@
  *   - severity_status: Indicates the severity status.
  *
  * @see template_preprocess_status_report()
- *
- * @ingroup themeable
  */
 #}
 <table class="system-status-report">
diff --git a/core/modules/system/templates/system-admin-index.html.twig b/core/themes/stable/templates/admin/system-admin-index.html.twig
similarity index 88%
copy from core/modules/system/templates/system-admin-index.html.twig
copy to core/themes/stable/templates/admin/system-admin-index.html.twig
index 17f8150..23178ee 100644
--- a/core/modules/system/templates/system-admin-index.html.twig
+++ b/core/themes/stable/templates/admin/system-admin-index.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for the admin index page.
+ * Theme override for the admin index page.
  *
  * Available variables:
  * - system_compact_link: Themed link to toggle compact view.
@@ -11,8 +11,6 @@
  *     through admin-block.html.twig.
  *
  * @see template_preprocess_system_admin_index()
- *
- * @ingroup themeable
  */
 #}
 <div class="admin clearfix">
diff --git a/core/modules/system/templates/system-config-form.html.twig b/core/themes/stable/templates/admin/system-config-form.html.twig
similarity index 81%
copy from core/modules/system/templates/system-config-form.html.twig
copy to core/themes/stable/templates/admin/system-config-form.html.twig
index 51e6fc7..8023813 100644
--- a/core/modules/system/templates/system-config-form.html.twig
+++ b/core/themes/stable/templates/admin/system-config-form.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a system settings form.
+ * Theme override for a system settings form.
  *
  * This template will be used when a system config form specifies 'config_form'
  * as its #theme callback.  Otherwise, by default, system config forms will be
@@ -10,8 +10,6 @@
  *
  * Available variables:
  * - form: The confirm form.
- *
- * @ingroup themeable
  */
 #}
 {{ form }}
diff --git a/core/modules/system/templates/system-modules-details.html.twig b/core/themes/stable/templates/admin/system-modules-details.html.twig
similarity index 97%
copy from core/modules/system/templates/system-modules-details.html.twig
copy to core/themes/stable/templates/admin/system-modules-details.html.twig
index e431c8e..618b58a 100644
--- a/core/modules/system/templates/system-modules-details.html.twig
+++ b/core/themes/stable/templates/admin/system-modules-details.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for the modules listing page.
+ * Theme override for the modules listing page.
  *
  * Displays a list of all packages in a project.
  *
@@ -20,8 +20,6 @@
  *   - links: A list of administration links provided by the module.
  *
  * @see template_preprocess_system_modules_details()
- *
- * @ingroup themeable
  */
 #}
 <table class="responsive-enabled" data-striping="1">
diff --git a/core/modules/system/templates/system-modules-uninstall.html.twig b/core/themes/stable/templates/admin/system-modules-uninstall.html.twig
similarity index 96%
copy from core/modules/system/templates/system-modules-uninstall.html.twig
copy to core/themes/stable/templates/admin/system-modules-uninstall.html.twig
index 180ca08..3556709 100644
--- a/core/modules/system/templates/system-modules-uninstall.html.twig
+++ b/core/themes/stable/templates/admin/system-modules-uninstall.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for the modules uninstall page.
+ * Theme override for the modules uninstall page.
  *
  * Available variables:
  * - form: The modules uninstall form.
@@ -17,8 +17,6 @@
  *     uninstalled.
  *
  * @see template_preprocess_system_modules_uninstall()
- *
- * @ingroup themeable
  */
 #}
 {{ form.filters }}
diff --git a/core/modules/system/templates/system-themes-page.html.twig b/core/themes/stable/templates/admin/system-themes-page.html.twig
similarity index 97%
copy from core/modules/system/templates/system-themes-page.html.twig
copy to core/themes/stable/templates/admin/system-themes-page.html.twig
index 6e65d76..5a23f1a 100644
--- a/core/modules/system/templates/system-themes-page.html.twig
+++ b/core/themes/stable/templates/admin/system-themes-page.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for the Appearance page.
+ * Theme override for the Appearance page.
  *
  * Available variables:
  * - attributes: HTML attributes for the main container.
@@ -26,8 +26,6 @@
  *       etc. these links should only be displayed if the theme is compatible.
  *
  * @see template_preprocess_system_themes_page()
- *
- * @ingroup themeable
  */
 #}
 <div{{ attributes }}>
diff --git a/core/modules/system/templates/tablesort-indicator.html.twig b/core/themes/stable/templates/admin/tablesort-indicator.html.twig
similarity index 82%
copy from core/modules/system/templates/tablesort-indicator.html.twig
copy to core/themes/stable/templates/admin/tablesort-indicator.html.twig
index 3601c6d..4e57274 100644
--- a/core/modules/system/templates/tablesort-indicator.html.twig
+++ b/core/themes/stable/templates/admin/tablesort-indicator.html.twig
@@ -1,14 +1,12 @@
 {#
 /**
  * @file
- * Default theme implementation for displaying a tablesort indicator.
+ * Theme override for displaying a tablesort indicator.
  *
  * Available variables:
  * - style: Either 'asc' or 'desc', indicating the sorting direction.
  *
  * @see template_preprocess_tablesort_indicator()
- *
- * @ingroup themeable
  */
 #}
 {%
diff --git a/core/modules/update/templates/update-last-check.html.twig b/core/themes/stable/templates/admin/update-last-check.html.twig
similarity index 81%
copy from core/modules/update/templates/update-last-check.html.twig
copy to core/themes/stable/templates/admin/update-last-check.html.twig
index 213f724..b94d6dc 100644
--- a/core/modules/update/templates/update-last-check.html.twig
+++ b/core/themes/stable/templates/admin/update-last-check.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for the last time update data was checked.
+ * Theme override for the last time update data was checked.
  *
  * Available variables:
  * - last: The timestamp that the site was last checked for updates.
@@ -9,8 +9,6 @@
  * - link: A link to check for updates manually.
  *
  * @see template_preprocess_update_last_check()
- *
- * @ingroup themeable
  */
 #}
 <p>
diff --git a/core/modules/update/templates/update-project-status.html.twig b/core/themes/stable/templates/admin/update-project-status.html.twig
similarity index 97%
copy from core/modules/update/templates/update-project-status.html.twig
copy to core/themes/stable/templates/admin/update-project-status.html.twig
index 4cc9a19..5a6d2ec 100644
--- a/core/modules/update/templates/update-project-status.html.twig
+++ b/core/themes/stable/templates/admin/update-project-status.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for the project status report.
+ * Theme override for the project status report.
  *
  * Available variables:
  * - title: The project title.
@@ -23,8 +23,6 @@
  * - disabled: The currently disabled projects in the project.
  *
  * @see template_preprocess_update_project_status()
- *
- * @ingroup themeable
  */
 #}
 {%
diff --git a/core/modules/update/templates/update-report.html.twig b/core/themes/stable/templates/admin/update-report.html.twig
similarity index 85%
copy from core/modules/update/templates/update-report.html.twig
copy to core/themes/stable/templates/admin/update-report.html.twig
index ae121cc..9efebc0 100644
--- a/core/modules/update/templates/update-report.html.twig
+++ b/core/themes/stable/templates/admin/update-report.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for the project status report.
+ * Theme override for the project status report.
  *
  * Available variables:
  * - last_checked: Themed last time update data was checked.
@@ -11,8 +11,6 @@
  *   - table: The project status table.
  *
  * @see template_preprocess_update_report()
- *
- * @ingroup themeable
  */
 #}
 {{ last_checked }}
diff --git a/core/modules/update/templates/update-version.html.twig b/core/themes/stable/templates/admin/update-version.html.twig
similarity index 93%
copy from core/modules/update/templates/update-version.html.twig
copy to core/themes/stable/templates/admin/update-version.html.twig
index 2d5520f..03a1c9d 100644
--- a/core/modules/update/templates/update-version.html.twig
+++ b/core/themes/stable/templates/admin/update-version.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for the version display of a project.
+ * Theme override for the version display of a project.
  *
  * Available variables:
  * - attributes: HTML attributes suitable for a container element.
@@ -13,8 +13,6 @@
  *   - release_link: The URL for the release notes.
  *
  * @see template_preprocess_update_version()
- *
- * @ingroup themeable
  */
 #}
 <div class="{{ attributes.class }} project-update__version"{{ attributes|without('class') }}>
diff --git a/core/modules/views_ui/templates/views-ui-build-group-filter-form.html.twig b/core/themes/stable/templates/admin/views-ui-build-group-filter-form.html.twig
similarity index 94%
copy from core/modules/views_ui/templates/views-ui-build-group-filter-form.html.twig
copy to core/themes/stable/templates/admin/views-ui-build-group-filter-form.html.twig
index 0e05c27..69e32ca 100644
--- a/core/modules/views_ui/templates/views-ui-build-group-filter-form.html.twig
+++ b/core/themes/stable/templates/admin/views-ui-build-group-filter-form.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for Views UI build group filter form.
+ * Theme override for Views UI build group filter form.
  *
  * Available variables:
  * - form: A render element representing the form. Contains the following:
@@ -19,8 +19,6 @@
  * - table: A rendered table element of the group filter form.
  *
  * @see template_preprocess_views_ui_build_group_filter_form()
- *
- * @ingroup themeable
  */
 #}
 {{ form.form_description }}
diff --git a/core/modules/views_ui/templates/views-ui-container.html.twig b/core/themes/stable/templates/admin/views-ui-container.html.twig
similarity index 73%
copy from core/modules/views_ui/templates/views-ui-container.html.twig
copy to core/themes/stable/templates/admin/views-ui-container.html.twig
index d45b158..e346966 100644
--- a/core/modules/views_ui/templates/views-ui-container.html.twig
+++ b/core/themes/stable/templates/admin/views-ui-container.html.twig
@@ -1,15 +1,13 @@
 {#
 /**
  * @file
- * Default theme implementation for a generic views UI container/wrapper.
+ * Theme override for a generic views UI container/wrapper.
  *
  * Available variables:
  * - attributes: HTML attributes to apply to the container element.
  * - children: The remaining elements such as dropbuttons and tabs.
  *
  * @see template_preprocess_views_ui_container()
- *
- * @ingroup themeable
  */
 #}
 <div{{ attributes }}>{{ children }}</div>
diff --git a/core/modules/views_ui/templates/views-ui-display-tab-bucket.html.twig b/core/themes/stable/templates/admin/views-ui-display-tab-bucket.html.twig
similarity index 89%
copy from core/modules/views_ui/templates/views-ui-display-tab-bucket.html.twig
copy to core/themes/stable/templates/admin/views-ui-display-tab-bucket.html.twig
index 88ab1bd..32dbdd7 100644
--- a/core/modules/views_ui/templates/views-ui-display-tab-bucket.html.twig
+++ b/core/themes/stable/templates/admin/views-ui-display-tab-bucket.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for each "box" on the display query edit screen.
+ * Theme override for each "box" on the display query edit screen.
  *
  * Available variables:
  * - attributes: HTML attributes to apply to the container element.
@@ -13,8 +13,6 @@
  *   default.
  *
  * @see template_preprocess_views_ui_display_tab_bucket()
- *
- * @ingroup themeable
  */
 #}
 {%
diff --git a/core/modules/views_ui/templates/views-ui-display-tab-setting.html.twig b/core/themes/stable/templates/admin/views-ui-display-tab-setting.html.twig
similarity index 91%
copy from core/modules/views_ui/templates/views-ui-display-tab-setting.html.twig
copy to core/themes/stable/templates/admin/views-ui-display-tab-setting.html.twig
index c90e5c9..77d659f 100644
--- a/core/modules/views_ui/templates/views-ui-display-tab-setting.html.twig
+++ b/core/themes/stable/templates/admin/views-ui-display-tab-setting.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for Views UI display tab settings.
+ * Theme override for Views UI display tab settings.
  *
  * Template for each row inside the "boxes" on the display query edit screen.
  *
@@ -14,8 +14,6 @@
  *   default.
  *
  * @see template_preprocess_views_ui_display_tab_setting()
- *
- * @ingroup themeable
  */
 #}
 {%
diff --git a/core/modules/views_ui/templates/views-ui-expose-filter-form.html.twig b/core/themes/stable/templates/admin/views-ui-expose-filter-form.html.twig
similarity index 94%
copy from core/modules/views_ui/templates/views-ui-expose-filter-form.html.twig
copy to core/themes/stable/templates/admin/views-ui-expose-filter-form.html.twig
index dfc4775..a23b6e2 100644
--- a/core/modules/views_ui/templates/views-ui-expose-filter-form.html.twig
+++ b/core/themes/stable/templates/admin/views-ui-expose-filter-form.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for exposed filter form.
+ * Theme override for exposed filter form.
  *
  * Available variables:
  * - form_description: The exposed filter's description.
@@ -15,8 +15,6 @@
  * - value: The filters available values.
  * - use_operator: Checkbox to allow the user to expose the operator.
  * - more: A details element for additional field exposed filter fields.
- *
- * @ingroup themeable
  */
 #}
 {{ form.form_description }}
diff --git a/core/modules/views_ui/templates/views-ui-rearrange-filter-form.html.twig b/core/themes/stable/templates/admin/views-ui-rearrange-filter-form.html.twig
similarity index 87%
copy from core/modules/views_ui/templates/views-ui-rearrange-filter-form.html.twig
copy to core/themes/stable/templates/admin/views-ui-rearrange-filter-form.html.twig
index b003a89..e38d132 100644
--- a/core/modules/views_ui/templates/views-ui-rearrange-filter-form.html.twig
+++ b/core/themes/stable/templates/admin/views-ui-rearrange-filter-form.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for Views UI rearrange filter form.
+ * Theme override for Views UI rearrange filter form.
  *
  * Available variables:
  * - form: A render element representing the form.
@@ -10,8 +10,6 @@
  * - table: The groupable filter table.
  *
  * @see template_preprocess_views_ui_rearrange_filter_form()
- *
- * @ingroup themeable
  */
 #}
 {{ form.override }}
diff --git a/core/modules/views_ui/templates/views-ui-style-plugin-table.html.twig b/core/themes/stable/templates/admin/views-ui-style-plugin-table.html.twig
similarity index 79%
copy from core/modules/views_ui/templates/views-ui-style-plugin-table.html.twig
copy to core/themes/stable/templates/admin/views-ui-style-plugin-table.html.twig
index 27463f5..2295390 100644
--- a/core/modules/views_ui/templates/views-ui-style-plugin-table.html.twig
+++ b/core/themes/stable/templates/admin/views-ui-style-plugin-table.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default template for the settings of a table style views display.
+ * Theme override for the settings of a table style views display.
  *
  * Available variables:
  * - table: A table of options for each field in this display.
@@ -9,8 +9,6 @@
  *   - description_markup: An overview for the settings of this display.
  *
  * @see template_preprocess_views_ui_style_plugin_table()
- *
- * @ingroup themeable
  */
 #}
 {{ form.description_markup }}
diff --git a/core/modules/views_ui/templates/views-ui-view-info.html.twig b/core/themes/stable/templates/admin/views-ui-view-info.html.twig
similarity index 84%
copy from core/modules/views_ui/templates/views-ui-view-info.html.twig
copy to core/themes/stable/templates/admin/views-ui-view-info.html.twig
index fa32a0c..1305234 100644
--- a/core/modules/views_ui/templates/views-ui-view-info.html.twig
+++ b/core/themes/stable/templates/admin/views-ui-view-info.html.twig
@@ -1,12 +1,10 @@
 {#
 /**
  * @file
- * Default theme implementation for basic administrative info about a View.
+ * Theme override for basic administrative info about a View.
  *
  * Available variables:
  * - displays: List of displays.
- *
- * @ingroup themeable
  */
 #}
 <h3 class="views-ui-view-title views-table-filter-text-source">{{ view.label }}</h3>
diff --git a/core/modules/views_ui/templates/views-ui-view-preview-section.html.twig b/core/themes/stable/templates/admin/views-ui-view-preview-section.html.twig
similarity index 82%
copy from core/modules/views_ui/templates/views-ui-view-preview-section.html.twig
copy to core/themes/stable/templates/admin/views-ui-view-preview-section.html.twig
index cfc840f..c2c83bd 100644
--- a/core/modules/views_ui/templates/views-ui-view-preview-section.html.twig
+++ b/core/themes/stable/templates/admin/views-ui-view-preview-section.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a views UI preview section.
+ * Theme override for a views UI preview section.
  *
  * Available variables:
  * - title: The human readable section title.
@@ -9,8 +9,6 @@
  * - content: The content for this section preview.
  *
  * @see template_preprocess_views_ui_view_preview_section()
- *
- * @ingroup themeable
  */
 #}
 <h1 class="section-title">{{ title }}</h1>
diff --git a/core/modules/system/templates/block--local-actions-block.html.twig b/core/themes/stable/templates/block/block--local-actions-block.html.twig
similarity index 79%
copy from core/modules/system/templates/block--local-actions-block.html.twig
copy to core/themes/stable/templates/block/block--local-actions-block.html.twig
index 65d57be..f272329 100644
--- a/core/modules/system/templates/block--local-actions-block.html.twig
+++ b/core/themes/stable/templates/block/block--local-actions-block.html.twig
@@ -1,4 +1,4 @@
-{% extends "@block/block.html.twig" %}
+{% extends "@stable/block/block.html.twig" %}
 {#
 /**
  * @file
diff --git a/core/modules/system/templates/block--system-branding-block.html.twig b/core/themes/stable/templates/block/block--system-branding-block.html.twig
similarity index 90%
copy from core/modules/system/templates/block--system-branding-block.html.twig
copy to core/themes/stable/templates/block/block--system-branding-block.html.twig
index 2a98687..186b360 100644
--- a/core/modules/system/templates/block--system-branding-block.html.twig
+++ b/core/themes/stable/templates/block/block--system-branding-block.html.twig
@@ -2,7 +2,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a branding block.
+ * Theme override for a branding block.
  *
  * Each branding element variable (logo, name, slogan) is only available if
  * enabled in the block configuration.
@@ -11,8 +11,6 @@
  * - site_logo: Logo for site as defined in Appearance or theme settings.
  * - site_name: Name for site as defined in Site information settings.
  * - site_slogan: Slogan for site as defined in Site information settings.
- *
- * @ingroup themeable
  */
 #}
 {% block content %}
diff --git a/core/modules/system/templates/block--system-menu-block.html.twig b/core/themes/stable/templates/block/block--system-menu-block.html.twig
similarity index 96%
copy from core/modules/system/templates/block--system-menu-block.html.twig
copy to core/themes/stable/templates/block/block--system-menu-block.html.twig
index 8f4548c..0919a88 100644
--- a/core/modules/system/templates/block--system-menu-block.html.twig
+++ b/core/themes/stable/templates/block/block--system-menu-block.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a menu block.
+ * Theme override for a menu block.
  *
  * Available variables:
  * - plugin_id: The ID of the block implementation.
@@ -29,8 +29,6 @@
  * to or skip the links.
  * See http://juicystudio.com/article/screen-readers-display-none.php and
  * http://www.w3.org/TR/WCAG-TECHS/H42.html for more information.
- *
- * @ingroup themeable
  */
 #}
 {% set heading_id = attributes.id ~ '-menu'|clean_id %}
diff --git a/core/modules/system/templates/block--system-messages-block.html.twig b/core/themes/stable/templates/block/block--system-messages-block.html.twig
similarity index 72%
copy from core/modules/system/templates/block--system-messages-block.html.twig
copy to core/themes/stable/templates/block/block--system-messages-block.html.twig
index f35af14..ef2e3ac 100644
--- a/core/modules/system/templates/block--system-messages-block.html.twig
+++ b/core/themes/stable/templates/block/block--system-messages-block.html.twig
@@ -1,15 +1,13 @@
 {#
 /**
  * @file
- * Default theme implementation for the messages block.
+ * Theme override for the messages block.
  *
  * Removes wrapper elements from block so that empty block does not appear when
  * there are no messages.
  *
  * Available variables:
  * - content: The content of this block.
- *
- * @ingroup themeable
  */
 #}
 {{ content }}
diff --git a/core/modules/block/templates/block.html.twig b/core/themes/stable/templates/block/block.html.twig
similarity index 94%
copy from core/modules/block/templates/block.html.twig
copy to core/themes/stable/templates/block/block.html.twig
index d880475..dca6f48 100644
--- a/core/modules/block/templates/block.html.twig
+++ b/core/themes/stable/templates/block/block.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation to display a block.
+ * Theme override to display a block.
  *
  * Available variables:
  * - plugin_id: The ID of the block implementation.
@@ -23,8 +23,6 @@
  *   displayed after the main title tag that appears in the template.
  *
  * @see template_preprocess_block()
- *
- * @ingroup themeable
  */
 #}
 <div{{ attributes }}>
diff --git a/core/themes/classy/templates/content-edit/file-managed-file.html.twig b/core/themes/stable/templates/content-edit/file-managed-file.html.twig
similarity index 91%
copy from core/themes/classy/templates/content-edit/file-managed-file.html.twig
copy to core/themes/stable/templates/content-edit/file-managed-file.html.twig
index e7ae48d..f639237 100644
--- a/core/themes/classy/templates/content-edit/file-managed-file.html.twig
+++ b/core/themes/stable/templates/content-edit/file-managed-file.html.twig
@@ -10,7 +10,6 @@
  * @see template_preprocess_file_managed_file()
  */
 #}
-{{ attach_library('classy/file') }}
 {%
   set classes = [
     'js-form-managed-file',
diff --git a/core/themes/classy/templates/content-edit/file-upload-help.html.twig b/core/themes/stable/templates/content-edit/file-upload-help.html.twig
similarity index 100%
copy from core/themes/classy/templates/content-edit/file-upload-help.html.twig
copy to core/themes/stable/templates/content-edit/file-upload-help.html.twig
diff --git a/core/themes/classy/templates/content-edit/file-widget-multiple.html.twig b/core/themes/stable/templates/content-edit/file-widget-multiple.html.twig
similarity index 100%
copy from core/themes/classy/templates/content-edit/file-widget-multiple.html.twig
copy to core/themes/stable/templates/content-edit/file-widget-multiple.html.twig
diff --git a/core/themes/classy/templates/content-edit/file-widget.html.twig b/core/themes/stable/templates/content-edit/file-widget.html.twig
similarity index 89%
copy from core/themes/classy/templates/content-edit/file-widget.html.twig
copy to core/themes/stable/templates/content-edit/file-widget.html.twig
index 23d03a1..55de590 100644
--- a/core/themes/classy/templates/content-edit/file-widget.html.twig
+++ b/core/themes/stable/templates/content-edit/file-widget.html.twig
@@ -10,7 +10,6 @@
  * @see template_preprocess_file_widget()
  */
 #}
-{{ attach_library('classy/file') }}
 <div{{ attributes }}>
   {{ element }}
 </div>
diff --git a/core/modules/filter/templates/filter-caption.html.twig b/core/themes/stable/templates/content-edit/filter-caption.html.twig
similarity index 90%
copy from core/modules/filter/templates/filter-caption.html.twig
copy to core/themes/stable/templates/content-edit/filter-caption.html.twig
index c90e35b..246cf0f 100644
--- a/core/modules/filter/templates/filter-caption.html.twig
+++ b/core/themes/stable/templates/content-edit/filter-caption.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a filter caption.
+ * Theme override for a filter caption.
  *
  * Returns HTML for a captioned image, audio, video or other tag.
  *
diff --git a/core/modules/filter/templates/filter-guidelines.html.twig b/core/themes/stable/templates/content-edit/filter-guidelines.html.twig
similarity index 87%
copy from core/modules/filter/templates/filter-guidelines.html.twig
copy to core/themes/stable/templates/content-edit/filter-guidelines.html.twig
index 317cfa6..4cd6706 100644
--- a/core/modules/filter/templates/filter-guidelines.html.twig
+++ b/core/themes/stable/templates/content-edit/filter-guidelines.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for guidelines for a text format.
+ * Theme override for guidelines for a text format.
  *
  * Available variables:
  * - format: Contains information about the current text format, including the
@@ -15,8 +15,6 @@
  *   formats.
  *
  * @see template_preprocess_filter_tips()
- *
- * @ingroup themeable
  */
 #}
 <div{{ attributes }}>
diff --git a/core/modules/filter/templates/filter-tips.html.twig b/core/themes/stable/templates/content-edit/filter-tips.html.twig
similarity index 92%
copy from core/modules/filter/templates/filter-tips.html.twig
copy to core/themes/stable/templates/content-edit/filter-tips.html.twig
index b9ed2d6..5163eda 100644
--- a/core/modules/filter/templates/filter-tips.html.twig
+++ b/core/themes/stable/templates/content-edit/filter-tips.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a set of filter tips.
+ * Theme override for a set of filter tips.
  *
  * Available variables:
  * - tips: Descriptions and a CSS ID in the form of 'module-name/filter-id'
@@ -14,8 +14,6 @@
  * - multiple: A flag indicating there is more than one filter tip.
  *
  * @see template_preprocess_filter_tips()
- *
- * @ingroup themeable
  */
 #}
 {% if multiple %}
diff --git a/core/modules/image/templates/image-widget.html.twig b/core/themes/stable/templates/content-edit/image-widget.html.twig
similarity index 81%
copy from core/modules/image/templates/image-widget.html.twig
copy to core/themes/stable/templates/content-edit/image-widget.html.twig
index 3a3d3da..cd3f60d 100644
--- a/core/modules/image/templates/image-widget.html.twig
+++ b/core/themes/stable/templates/content-edit/image-widget.html.twig
@@ -1,15 +1,13 @@
 {#
 /**
  * @file
- * Default theme implementation for an image field widget.
+ * Theme override for an image field widget.
  *
  * Available variables:
  * - attributes: HTML attributes for the containing element.
  * - data: Render elements of the image widget.
  *
  * @see template_preprocess_image_widget()
- *
- * @ingroup themeable
  */
 #}
 <div{{ attributes }}>
diff --git a/core/themes/classy/templates/content-edit/node-add-list.html.twig b/core/themes/stable/templates/content-edit/node-add-list.html.twig
similarity index 96%
copy from core/themes/classy/templates/content-edit/node-add-list.html.twig
copy to core/themes/stable/templates/content-edit/node-add-list.html.twig
index f38fe3a..560b9e3 100644
--- a/core/themes/classy/templates/content-edit/node-add-list.html.twig
+++ b/core/themes/stable/templates/content-edit/node-add-list.html.twig
@@ -14,7 +14,7 @@
  */
 #}
 {% if types is not empty %}
-  <dl class="node-type-list">
+  <dl>
     {% for type in types %}
       <dt>{{ type.add_link }}</dt>
       <dd>{{ type.description }}</dd>
diff --git a/core/modules/node/templates/node-edit-form.html.twig b/core/themes/stable/templates/content-edit/node-edit-form.html.twig
similarity index 82%
copy from core/modules/node/templates/node-edit-form.html.twig
copy to core/themes/stable/templates/content-edit/node-edit-form.html.twig
index fa455e6..db74a20 100644
--- a/core/modules/node/templates/node-edit-form.html.twig
+++ b/core/themes/stable/templates/content-edit/node-edit-form.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a node edit form.
+ * Theme override for a node edit form.
  *
  * Two column template for the node add/edit form.
  *
@@ -13,8 +13,6 @@
  * - form: The node add/edit form.
  *
  * @see seven_form_node_form_alter()
- *
- * @ingroup themeable
  */
 #}
 {{ form }}
diff --git a/core/modules/filter/templates/text-format-wrapper.html.twig b/core/themes/stable/templates/content-edit/text-format-wrapper.html.twig
similarity index 84%
copy from core/modules/filter/templates/text-format-wrapper.html.twig
copy to core/themes/stable/templates/content-edit/text-format-wrapper.html.twig
index de61d92..33ca7ce 100644
--- a/core/modules/filter/templates/text-format-wrapper.html.twig
+++ b/core/themes/stable/templates/content-edit/text-format-wrapper.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a text format-enabled form element.
+ * Theme override for a text format-enabled form element.
  *
  * Available variables:
  * - children: Text format element children.
@@ -11,8 +11,6 @@
  *   added to the description container.
  *
  * @see template_preprocess_text_format_wrapper()
- *
- * @ingroup themeable
  */
 #}
 <div class="js-text-format-wrapper js-form-item form-item">
diff --git a/core/themes/classy/templates/content/aggregator-item.html.twig b/core/themes/stable/templates/content/aggregator-item.html.twig
similarity index 87%
copy from core/themes/classy/templates/content/aggregator-item.html.twig
copy to core/themes/stable/templates/content/aggregator-item.html.twig
index 20f6d7c..f60bdde 100644
--- a/core/themes/classy/templates/content/aggregator-item.html.twig
+++ b/core/themes/stable/templates/content/aggregator-item.html.twig
@@ -14,9 +14,9 @@
  * @see template_preprocess_aggregator_item()
  */
 #}
-<article{{ attributes.addClass('aggregator-item') }}>
+<article{{ attributes }}>
   {{ title_prefix }}
-  <h3 class="feed-item-title">
+  <h3>
     <a href="{{ url }}">{{ title }}</a>
   </h3>
   {{ title_suffix }}
diff --git a/core/themes/classy/templates/content/book-node-export-html.html.twig b/core/themes/stable/templates/content/book-node-export-html.html.twig
similarity index 80%
copy from core/themes/classy/templates/content/book-node-export-html.html.twig
copy to core/themes/stable/templates/content/book-node-export-html.html.twig
index 94a4c24..ff11149 100644
--- a/core/themes/classy/templates/content/book-node-export-html.html.twig
+++ b/core/themes/stable/templates/content/book-node-export-html.html.twig
@@ -13,8 +13,8 @@
  * @see template_preprocess_book_node_export_html()
  */
 #}
-<article id="node-{{ node.id }}" class="section-{{ depth }}">
-  <h1 class="book-heading">{{ title }}</h1>
+<article>
+  <h1>{{ title }}</h1>
   {{ content }}
   {{ children }}
 </article>
diff --git a/core/modules/comment/templates/comment.html.twig b/core/themes/stable/templates/content/comment.html.twig
similarity index 98%
copy from core/modules/comment/templates/comment.html.twig
copy to core/themes/stable/templates/content/comment.html.twig
index 14c52eb..ffc1d9c 100644
--- a/core/modules/comment/templates/comment.html.twig
+++ b/core/themes/stable/templates/content/comment.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for comments.
+ * Theme override for comments.
  *
  * Available variables:
  * - author: Comment author. Can be a link or plain text.
@@ -62,8 +62,6 @@
  * - entity: Entity the comments are attached to.
  *
  * @see template_preprocess_comment()
- *
- * @ingroup themeable
  */
 #}
 
diff --git a/core/themes/classy/templates/content/mark.html.twig b/core/themes/stable/templates/content/mark.html.twig
similarity index 80%
copy from core/themes/classy/templates/content/mark.html.twig
copy to core/themes/stable/templates/content/mark.html.twig
index 9219915..bc70b5c 100644
--- a/core/themes/classy/templates/content/mark.html.twig
+++ b/core/themes/stable/templates/content/mark.html.twig
@@ -13,8 +13,8 @@
 #}
 {% if logged_in %}
   {% if status is constant('MARK_NEW') %}
-    <span class="marker">{{ 'New'|t }}</span>
+    {{ 'New'|t }}
   {% elseif status is constant('MARK_UPDATED') %}
-    <span class="marker">{{ 'Updated'|t }}</span>
+    {{ 'Updated'|t }}
   {% endif %}
 {% endif %}
diff --git a/core/modules/node/templates/node.html.twig b/core/themes/stable/templates/content/node.html.twig
similarity index 98%
copy from core/modules/node/templates/node.html.twig
copy to core/themes/stable/templates/content/node.html.twig
index e7e353d..68a92ea 100644
--- a/core/modules/node/templates/node.html.twig
+++ b/core/themes/stable/templates/content/node.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation to display a node.
+ * Theme override to display a node.
  *
  * Available variables:
  * - node: The node entity with limited access to object properties and methods.
@@ -61,8 +61,6 @@
  * @todo Remove the id attribute (or make it a class), because if that gets
  *   rendered twice on a page this is invalid CSS for example: two lists
  *   in different view modes.
- *
- * @ingroup themeable
  */
 #}
 <article{{ attributes }}>
diff --git a/core/themes/classy/templates/content/page-title.html.twig b/core/themes/stable/templates/content/page-title.html.twig
similarity index 90%
copy from core/themes/classy/templates/content/page-title.html.twig
copy to core/themes/stable/templates/content/page-title.html.twig
index adec853..bdeded4 100644
--- a/core/themes/classy/templates/content/page-title.html.twig
+++ b/core/themes/stable/templates/content/page-title.html.twig
@@ -16,6 +16,6 @@
 #}
 {{ title_prefix }}
 {% if title %}
-  <h1{{ title_attributes.addClass('page-title') }}>{{ title }}</h1>
+  <h1{{ title_attributes }}>{{ title }}</h1>
 {% endif %}
 {{ title_suffix }}
diff --git a/core/modules/search/templates/search-result.html.twig b/core/themes/stable/templates/content/search-result.html.twig
similarity index 96%
copy from core/modules/search/templates/search-result.html.twig
copy to core/themes/stable/templates/content/search-result.html.twig
index 8982e90..adf8134 100644
--- a/core/modules/search/templates/search-result.html.twig
+++ b/core/themes/stable/templates/content/search-result.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for displaying a single search result.
+ * Theme override for displaying a single search result.
  *
  * This template renders a single search result. The list of results is
  * rendered using '#theme' => 'item_list', with suggestions of:
@@ -54,8 +54,6 @@
  * @endcode
  *
  * @see template_preprocess_search_result()
- *
- * @ingroup themeable
  */
 #}
 {{ title_prefix }}
diff --git a/core/modules/taxonomy/templates/taxonomy-term.html.twig b/core/themes/stable/templates/content/taxonomy-term.html.twig
similarity index 91%
copy from core/modules/taxonomy/templates/taxonomy-term.html.twig
copy to core/themes/stable/templates/content/taxonomy-term.html.twig
index d6fb9bd..09c242b 100644
--- a/core/modules/taxonomy/templates/taxonomy-term.html.twig
+++ b/core/themes/stable/templates/content/taxonomy-term.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation to display a taxonomy term.
+ * Theme override to display a taxonomy term.
  *
  * Available variables:
  * - url: URL of the current term.
@@ -21,8 +21,6 @@
  * - view_mode: View mode, e.g. 'full', 'teaser', etc.
  *
  * @see template_preprocess_taxonomy_term()
- *
- * @ingroup themeable
  */
 #}
 <div{{ attributes}}>
diff --git a/core/modules/aggregator/templates/aggregator-feed.html.twig b/core/themes/stable/templates/dataset/aggregator-feed.html.twig
similarity index 87%
copy from core/modules/aggregator/templates/aggregator-feed.html.twig
copy to core/themes/stable/templates/dataset/aggregator-feed.html.twig
index ee44c35..7ad0790 100644
--- a/core/modules/aggregator/templates/aggregator-feed.html.twig
+++ b/core/themes/stable/templates/dataset/aggregator-feed.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation to present an aggregator feed.
+ * Theme override to present an aggregator feed.
  *
  * The contents are rendered above feed listings when browsing source feeds.
  * For example, "example.com/aggregator/sources/1".
@@ -14,8 +14,6 @@
  *   of a given element.
  *
  * @see template_preprocess_aggregator_feed()
- *
- * @ingroup themeable
  */
 #}
 {{ title_prefix }}
diff --git a/core/modules/forum/templates/forum-icon.html.twig b/core/themes/stable/templates/dataset/forum-icon.html.twig
similarity index 88%
copy from core/modules/forum/templates/forum-icon.html.twig
copy to core/themes/stable/templates/dataset/forum-icon.html.twig
index 8a5e325..37a970e 100644
--- a/core/modules/forum/templates/forum-icon.html.twig
+++ b/core/themes/stable/templates/dataset/forum-icon.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation to display a status icon for a forum post.
+ * Theme override to display a status icon for a forum post.
  *
  * Available variables:
  * - attributes: HTML attributes to be applied to the wrapper element.
@@ -14,8 +14,6 @@
  * - icon_status: Indicates which status icon should be used.
  *
  * @see template_preprocess_forum_icon()
- *
- * @ingroup themeable
  */
 #}
 <div{{ attributes }}>
diff --git a/core/modules/forum/templates/forum-list.html.twig b/core/themes/stable/templates/dataset/forum-list.html.twig
similarity index 96%
copy from core/modules/forum/templates/forum-list.html.twig
copy to core/themes/stable/templates/dataset/forum-list.html.twig
index c2e5567..3de920a 100644
--- a/core/modules/forum/templates/forum-list.html.twig
+++ b/core/themes/stable/templates/dataset/forum-list.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation to display a list of forums and containers.
+ * Theme override to display a list of forums and containers.
  *
  * Available variables:
  * - forums: A collection of forums and containers to display. It is keyed to
@@ -28,8 +28,6 @@
  *   forums array.
  *
  * @see template_preprocess_forum_list()
- *
- * @ingroup themeable
  */
 #}
 <table>
diff --git a/core/modules/forum/templates/forums.html.twig b/core/themes/stable/templates/dataset/forums.html.twig
similarity index 85%
copy from core/modules/forum/templates/forums.html.twig
copy to core/themes/stable/templates/dataset/forums.html.twig
index 5116c76..1871187 100644
--- a/core/modules/forum/templates/forums.html.twig
+++ b/core/themes/stable/templates/dataset/forums.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation to display a forum.
+ * Theme override to display a forum.
  *
  * May contain forum containers as well as forum topics.
  *
@@ -12,8 +12,6 @@
  * - forums_defined: A flag to indicate that the forums are configured.
  *
  * @see template_preprocess_forums()
- *
- * @ingroup themeable
  */
 #}
 {% if forums_defined %}
diff --git a/core/modules/system/templates/item-list.html.twig b/core/themes/stable/templates/dataset/item-list.html.twig
similarity index 94%
copy from core/modules/system/templates/item-list.html.twig
copy to core/themes/stable/templates/dataset/item-list.html.twig
index 1462cf4..86cc636 100644
--- a/core/modules/system/templates/item-list.html.twig
+++ b/core/themes/stable/templates/dataset/item-list.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for an item list.
+ * Theme override for an item list.
  *
  * Available variables:
  * - items: A list of items. Each item contains:
@@ -17,8 +17,6 @@
  *   - list_style: The custom list style.
  *
  * @see template_preprocess_item_list()
- *
- * @ingroup themeable
  */
 #}
 {% if context.list_style %}
diff --git a/core/modules/system/templates/table.html.twig b/core/themes/stable/templates/dataset/table.html.twig
similarity index 97%
copy from core/modules/system/templates/table.html.twig
copy to core/themes/stable/templates/dataset/table.html.twig
index f6b32e4..b7267be 100644
--- a/core/modules/system/templates/table.html.twig
+++ b/core/themes/stable/templates/dataset/table.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation to display a table.
+ * Theme override to display a table.
  *
  * Available variables:
  * - attributes: HTML attributes to apply to the <table> tag.
@@ -37,8 +37,6 @@
  * - header_columns: The number of columns in the header.
  *
  * @see template_preprocess_table()
- *
- * @ingroup themeable
  */
 #}
 <table{{ attributes }}>
diff --git a/core/modules/comment/templates/field--comment.html.twig b/core/themes/stable/templates/field/field--comment.html.twig
similarity index 96%
copy from core/modules/comment/templates/field--comment.html.twig
copy to core/themes/stable/templates/field/field--comment.html.twig
index 879f4d5..33a60ae 100644
--- a/core/modules/comment/templates/field--comment.html.twig
+++ b/core/themes/stable/templates/field/field--comment.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme override for comment fields.
+ * Theme override for comment fields.
  *
  * Available variables:
  * - attributes: HTML attributes for the containing element.
diff --git a/core/modules/node/templates/field--node--created.html.twig b/core/themes/stable/templates/field/field--node--created.html.twig
similarity index 89%
copy from core/modules/node/templates/field--node--created.html.twig
copy to core/themes/stable/templates/field/field--node--created.html.twig
index 049144f..e00837d 100644
--- a/core/modules/node/templates/field--node--created.html.twig
+++ b/core/themes/stable/templates/field/field--node--created.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for the node created field.
+ * Theme override for the node created field.
  *
  * This is an override of field.html.twig for the node created field. See that
  * template for documentation about its details and overrides.
@@ -17,8 +17,6 @@
  * - label_display: The display settings for the label.
  *
  * @see field.html.twig
- *
- * @ingroup themeable
  */
 #}
 <span{{ attributes }}>
diff --git a/core/modules/node/templates/field--node--title.html.twig b/core/themes/stable/templates/field/field--node--title.html.twig
similarity index 89%
copy from core/modules/node/templates/field--node--title.html.twig
copy to core/themes/stable/templates/field/field--node--title.html.twig
index 68142ca..5ab974f 100644
--- a/core/modules/node/templates/field--node--title.html.twig
+++ b/core/themes/stable/templates/field/field--node--title.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for the node title field.
+ * Theme override for the node title field.
  *
  * This is an override of field.html.twig for the node title field. See that
  * template for documentation about its details and overrides.
@@ -17,8 +17,6 @@
  * - label_display: The display settings for the label.
  *
  * @see field.html.twig
- *
- * @ingroup themeable
  */
 #}
 <span{{ attributes }}>
diff --git a/core/modules/node/templates/field--node--uid.html.twig b/core/themes/stable/templates/field/field--node--uid.html.twig
similarity index 90%
copy from core/modules/node/templates/field--node--uid.html.twig
copy to core/themes/stable/templates/field/field--node--uid.html.twig
index 91a97b3..af730dc 100644
--- a/core/modules/node/templates/field--node--uid.html.twig
+++ b/core/themes/stable/templates/field/field--node--uid.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for the node user field.
+ * Theme override for the node user field.
  *
  * This is an override of field.html.twig for the node user field. See that
  * template for documentation about its details and overrides.
@@ -17,8 +17,6 @@
  * - label_display: The display settings for the label.
  *
  * @see field.html.twig
- *
- * @ingroup themeable
  */
 #}
 <span{{ attributes }}>
diff --git a/core/modules/system/templates/field.html.twig b/core/themes/stable/templates/field/field.html.twig
similarity index 96%
copy from core/modules/system/templates/field.html.twig
copy to core/themes/stable/templates/field/field.html.twig
index babc512..05d6e82 100644
--- a/core/modules/system/templates/field.html.twig
+++ b/core/themes/stable/templates/field/field.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a field.
+ * Theme override for a field.
  *
  * To override output, copy the "field.html.twig" from the templates directory
  * to your theme's directory and customize it, just like customizing other
@@ -34,8 +34,6 @@
  * - label_display: The display settings for the label.
  *
  * @see template_preprocess_field()
- *
- * @ingroup themeable
  */
 #}
 
diff --git a/core/modules/file/templates/file-link.html.twig b/core/themes/stable/templates/field/file-link.html.twig
similarity index 74%
copy from core/modules/file/templates/file-link.html.twig
copy to core/themes/stable/templates/field/file-link.html.twig
index 44cbd7f..0424830 100644
--- a/core/modules/file/templates/file-link.html.twig
+++ b/core/themes/stable/templates/field/file-link.html.twig
@@ -1,15 +1,13 @@
 {#
 /**
  * @file
- * Default theme implementation for a link to a file.
+ * Theme override for a link to a file.
  *
  * Available variables:
  * - attributes: The HTML attributes for the containing element.
  * - link: A link to the file.
  *
  * @see template_preprocess_file_link()
- *
- * @ingroup themeable
  */
 #}
 <span{{ attributes }}>{{ link }}</span>
diff --git a/core/themes/classy/templates/field/image-formatter.html.twig b/core/themes/stable/templates/field/image-formatter.html.twig
similarity index 83%
copy from core/themes/classy/templates/field/image-formatter.html.twig
copy to core/themes/stable/templates/field/image-formatter.html.twig
index 04a98a3..d0390c0 100644
--- a/core/themes/classy/templates/field/image-formatter.html.twig
+++ b/core/themes/stable/templates/field/image-formatter.html.twig
@@ -6,7 +6,6 @@
  * Available variables:
  * - image: A collection of image data.
  * - image_style: An optional image style.
- * - path: An optional array containing the link 'path' and link 'options'.
  * - url: An optional URL the image can be linked to.
  *
  * @see template_preprocess_image_formatter()
diff --git a/core/themes/classy/templates/field/image-style.html.twig b/core/themes/stable/templates/field/image-style.html.twig
similarity index 100%
copy from core/themes/classy/templates/field/image-style.html.twig
copy to core/themes/stable/templates/field/image-style.html.twig
diff --git a/core/modules/system/templates/image.html.twig b/core/themes/stable/templates/field/image.html.twig
similarity index 76%
copy from core/modules/system/templates/image.html.twig
copy to core/themes/stable/templates/field/image.html.twig
index 6411eaa..b342eee 100644
--- a/core/modules/system/templates/image.html.twig
+++ b/core/themes/stable/templates/field/image.html.twig
@@ -1,15 +1,13 @@
 {#
 /**
  * @file
- * Default theme implementation of an image.
+ * Theme override of an image.
  *
  * Available variables:
  * - attributes: HTML attributes for the img tag.
  * - style_name: (optional) The name of the image style applied.
  *
  * @see template_preprocess_image()
- *
- * @ingroup themeable
  */
 #}
 <img{{ attributes }} />
diff --git a/core/modules/link/templates/link-formatter-link-separate.html.twig b/core/themes/stable/templates/field/link-formatter-link-separate.html.twig
similarity index 78%
copy from core/modules/link/templates/link-formatter-link-separate.html.twig
copy to core/themes/stable/templates/field/link-formatter-link-separate.html.twig
index 469cd9a..0aa1b4a 100644
--- a/core/modules/link/templates/link-formatter-link-separate.html.twig
+++ b/core/themes/stable/templates/field/link-formatter-link-separate.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation of a link with separate title and URL elements.
+ * Theme override of a link with separate title and URL elements.
  *
  * Available variables:
  * - link: The link that has already been formatted by l().
@@ -10,8 +10,6 @@
  *
  * @see template_preprocess()
  * @see template_preprocess_link_formatter_link_separate()
- *
- * @ingroup themeable
  */
 #}
 {% spaceless %}
diff --git a/core/modules/responsive_image/templates/responsive-image-formatter.html.twig b/core/themes/stable/templates/field/responsive-image-formatter.html.twig
similarity index 76%
copy from core/modules/responsive_image/templates/responsive-image-formatter.html.twig
copy to core/themes/stable/templates/field/responsive-image-formatter.html.twig
index 93caba8..3f30260 100644
--- a/core/modules/responsive_image/templates/responsive-image-formatter.html.twig
+++ b/core/themes/stable/templates/field/responsive-image-formatter.html.twig
@@ -1,15 +1,13 @@
 {#
 /**
  * @file
- * Default theme implementation to display a formatted responsive image field.
+ * Theme override to display a formatted responsive image field.
  *
  * Available variables:
  * - responsive_image: A collection of responsive image data.
  * - url: An optional URL the image can be linked to.
  *
  * @see template_preprocess_responsive_image_formatter()
- *
- * @ingroup themeable
  */
 #}
 {% if url %}
diff --git a/core/modules/responsive_image/templates/responsive-image.html.twig b/core/themes/stable/templates/field/responsive-image.html.twig
similarity index 92%
copy from core/modules/responsive_image/templates/responsive-image.html.twig
copy to core/themes/stable/templates/field/responsive-image.html.twig
index 99fca6b..ae77ffb 100644
--- a/core/modules/responsive_image/templates/responsive-image.html.twig
+++ b/core/themes/stable/templates/field/responsive-image.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation of a responsive image.
+ * Theme override of a responsive image.
  *
  * Available variables:
  * - sources: The attributes of the <source> tags for this <picture> tag.
@@ -11,8 +11,6 @@
  *
  * @see template_preprocess()
  * @see template_preprocess_responsive_image()
- *
- * @ingroup themeable
  */
 #}
 {% if output_image_tag %}
diff --git a/core/modules/system/templates/time.html.twig b/core/themes/stable/templates/field/time.html.twig
similarity index 93%
copy from core/modules/system/templates/time.html.twig
copy to core/themes/stable/templates/field/time.html.twig
index 9fc2dfa..cb93f9d 100644
--- a/core/modules/system/templates/time.html.twig
+++ b/core/themes/stable/templates/field/time.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a date / time element.
+ * Theme override for a date / time element.
  *
  * Available variables
  * - timestamp: (optional) A UNIX timestamp for the datetime attribute. If the
diff --git a/core/themes/classy/templates/form/checkboxes.html.twig b/core/themes/stable/templates/form/checkboxes.html.twig
similarity index 100%
copy from core/themes/classy/templates/form/checkboxes.html.twig
copy to core/themes/stable/templates/form/checkboxes.html.twig
diff --git a/core/themes/classy/templates/form/confirm-form.html.twig b/core/themes/stable/templates/form/confirm-form.html.twig
similarity index 100%
copy from core/themes/classy/templates/form/confirm-form.html.twig
copy to core/themes/stable/templates/form/confirm-form.html.twig
diff --git a/core/themes/classy/templates/form/container.html.twig b/core/themes/stable/templates/form/container.html.twig
similarity index 100%
copy from core/themes/classy/templates/form/container.html.twig
copy to core/themes/stable/templates/form/container.html.twig
diff --git a/core/themes/classy/templates/form/datetime-form.html.twig b/core/themes/stable/templates/form/datetime-form.html.twig
similarity index 84%
copy from core/themes/classy/templates/form/datetime-form.html.twig
copy to core/themes/stable/templates/form/datetime-form.html.twig
index f56182f..1a26f11 100644
--- a/core/themes/classy/templates/form/datetime-form.html.twig
+++ b/core/themes/stable/templates/form/datetime-form.html.twig
@@ -10,6 +10,6 @@
  * @see template_preprocess_datetime_form()
  */
 #}
-<div{{ attributes.addClass('container-inline') }}>
+<div{{ attributes }}>
   {{ content }}
 </div>
diff --git a/core/modules/system/templates/datetime-wrapper.html.twig b/core/themes/stable/templates/form/datetime-wrapper.html.twig
similarity index 89%
copy from core/modules/system/templates/datetime-wrapper.html.twig
copy to core/themes/stable/templates/form/datetime-wrapper.html.twig
index 8430baa..3c37ffd 100644
--- a/core/modules/system/templates/datetime-wrapper.html.twig
+++ b/core/themes/stable/templates/form/datetime-wrapper.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation of a datetime form wrapper.
+ * Theme override of a datetime form wrapper.
  *
  * Available variables:
  * - content: The form element to be output, usually a datelist, or datetime.
@@ -11,8 +11,6 @@
  * - required: An indicator for whether the associated form element is required.
  *
  * @see template_preprocess_datetime_wrapper()
- *
- * @ingroup themeable
  */
 #}
 {%
diff --git a/core/modules/system/templates/details.html.twig b/core/themes/stable/templates/form/details.html.twig
similarity index 90%
copy from core/modules/system/templates/details.html.twig
copy to core/themes/stable/templates/form/details.html.twig
index cf50eb0..f4c99e1 100644
--- a/core/modules/system/templates/details.html.twig
+++ b/core/themes/stable/templates/form/details.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a details element.
+ * Theme override for a details element.
  *
  * Available variables
  * - attributes: A list of HTML attributes for the details element.
@@ -12,8 +12,6 @@
  * - value: (optional) The value of the element, may not be set.
  *
  * @see template_preprocess_details()
- *
- * @ingroup themeable
  */
 #}
 <details{{ attributes }}>
diff --git a/core/themes/classy/templates/form/dropbutton-wrapper.html.twig b/core/themes/stable/templates/form/dropbutton-wrapper.html.twig
similarity index 100%
copy from core/themes/classy/templates/form/dropbutton-wrapper.html.twig
copy to core/themes/stable/templates/form/dropbutton-wrapper.html.twig
diff --git a/core/themes/classy/templates/form/field-multiple-value-form.html.twig b/core/themes/stable/templates/form/field-multiple-value-form.html.twig
similarity index 100%
copy from core/themes/classy/templates/form/field-multiple-value-form.html.twig
copy to core/themes/stable/templates/form/field-multiple-value-form.html.twig
diff --git a/core/themes/classy/templates/form/fieldset.html.twig b/core/themes/stable/templates/form/fieldset.html.twig
similarity index 95%
copy from core/themes/classy/templates/form/fieldset.html.twig
copy to core/themes/stable/templates/form/fieldset.html.twig
index 4bd7d0a..8f1f73d 100644
--- a/core/themes/classy/templates/form/fieldset.html.twig
+++ b/core/themes/stable/templates/form/fieldset.html.twig
@@ -42,8 +42,8 @@
   </legend>
   <div class="fieldset-wrapper">
     {% if errors %}
-      <div class="form-item--error-message">
-        <strong>{{ errors }}</strong>
+      <div>
+        {{ errors }}
       </div>
     {% endif %}
     {% if prefix %}
diff --git a/core/themes/classy/templates/form/form-element-label.html.twig b/core/themes/stable/templates/form/form-element-label.html.twig
similarity index 100%
copy from core/themes/classy/templates/form/form-element-label.html.twig
copy to core/themes/stable/templates/form/form-element-label.html.twig
diff --git a/core/themes/classy/templates/form/form-element.html.twig b/core/themes/stable/templates/form/form-element.html.twig
similarity index 98%
copy from core/themes/classy/templates/form/form-element.html.twig
copy to core/themes/stable/templates/form/form-element.html.twig
index 3bde4f7..9e87a1b 100644
--- a/core/themes/classy/templates/form/form-element.html.twig
+++ b/core/themes/stable/templates/form/form-element.html.twig
@@ -49,9 +49,8 @@
     'js-form-item',
     'form-item',
     'js-form-type-' ~ type|clean_class,
-    'form-type-' ~ type|clean_class,
-    'js-form-item-' ~ name|clean_class,
     'form-item-' ~ name|clean_class,
+    'js-form-item-' ~ name|clean_class,
     title_display not in ['after', 'before'] ? 'form-no-label',
     disabled == 'disabled' ? 'form-disabled',
     errors ? 'form-item--error',
@@ -84,7 +83,7 @@
   {% endif %}
   {% if errors %}
     <div class="form-item--error-message">
-      <strong>{{ errors }}</strong>
+      {{ errors }}
     </div>
   {% endif %}
   {% if description_display in ['after', 'invisible'] and description.content %}
diff --git a/core/themes/classy/templates/form/form.html.twig b/core/themes/stable/templates/form/form.html.twig
similarity index 100%
copy from core/themes/classy/templates/form/form.html.twig
copy to core/themes/stable/templates/form/form.html.twig
diff --git a/core/themes/classy/templates/form/input.html.twig b/core/themes/stable/templates/form/input.html.twig
similarity index 100%
copy from core/themes/classy/templates/form/input.html.twig
copy to core/themes/stable/templates/form/input.html.twig
diff --git a/core/themes/classy/templates/form/radios.html.twig b/core/themes/stable/templates/form/radios.html.twig
similarity index 78%
copy from core/themes/classy/templates/form/radios.html.twig
copy to core/themes/stable/templates/form/radios.html.twig
index 2e4bafd..6e9a9d7 100644
--- a/core/themes/classy/templates/form/radios.html.twig
+++ b/core/themes/stable/templates/form/radios.html.twig
@@ -10,4 +10,4 @@
  * @see template_preprocess_radios()
  */
 #}
-<div{{ attributes.addClass('form-radios') }}>{{ children }}</div>
+<div{{ attributes }}>{{ children }}</div>
diff --git a/core/themes/classy/templates/form/select.html.twig b/core/themes/stable/templates/form/select.html.twig
similarity index 100%
copy from core/themes/classy/templates/form/select.html.twig
copy to core/themes/stable/templates/form/select.html.twig
diff --git a/core/modules/system/templates/textarea.html.twig b/core/themes/stable/templates/form/textarea.html.twig
similarity index 83%
copy from core/modules/system/templates/textarea.html.twig
copy to core/themes/stable/templates/form/textarea.html.twig
index 6a1a46e..9767bc5 100644
--- a/core/modules/system/templates/textarea.html.twig
+++ b/core/themes/stable/templates/form/textarea.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a 'textarea' #type form element.
+ * Theme override for a 'textarea' #type form element.
  *
  * Available variables
  * - wrapper_attributes: A list of HTML attributes for the wrapper element.
@@ -11,8 +11,6 @@
  * - value: The textarea content.
  *
  * @see template_preprocess_textarea()
- *
- * @ingroup themeable
  */
 #}
 <div{{ wrapper_attributes }}>
diff --git a/core/themes/classy/templates/layout/book-export-html.html.twig b/core/themes/stable/templates/layout/book-export-html.html.twig
similarity index 97%
copy from core/themes/classy/templates/layout/book-export-html.html.twig
copy to core/themes/stable/templates/layout/book-export-html.html.twig
index ea33648..17ac1bc 100644
--- a/core/themes/classy/templates/layout/book-export-html.html.twig
+++ b/core/themes/stable/templates/layout/book-export-html.html.twig
@@ -35,7 +35,7 @@
     #}
 
   {% for i in 1..depth-1 if depth > 1 %}
-    <div class="section-{{ i }}">
+    <div>
   {% endfor %}
   {{ contents }}
   {% for i in 1..depth-1 if depth > 1 %}
diff --git a/core/modules/system/templates/html.html.twig b/core/themes/stable/templates/layout/html.html.twig
similarity index 93%
copy from core/modules/system/templates/html.html.twig
copy to core/themes/stable/templates/layout/html.html.twig
index 39702c2..4577ac5 100644
--- a/core/modules/system/templates/html.html.twig
+++ b/core/themes/stable/templates/layout/html.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for the basic structure of a single Drupal page.
+ * Theme override for the basic structure of a single Drupal page.
  *
  * Variables:
  * - logged_in: A flag indicating if user is logged in.
@@ -21,8 +21,6 @@
  *   placeholders.
  *
  * @see template_preprocess_html()
- *
- * @ingroup themeable
  */
 #}
 <!DOCTYPE html>
diff --git a/core/modules/system/templates/install-page.html.twig b/core/themes/stable/templates/layout/install-page.html.twig
similarity index 93%
copy from core/modules/system/templates/install-page.html.twig
copy to core/themes/stable/templates/layout/install-page.html.twig
index 1d0e479..44341f4 100644
--- a/core/modules/system/templates/install-page.html.twig
+++ b/core/themes/stable/templates/layout/install-page.html.twig
@@ -1,14 +1,12 @@
 {#
 /**
  * @file
- * Default theme implementation to display a Drupal installation page.
+ * Theme override to display a Drupal installation page.
  *
  * All available variables are mirrored in page.html.twig.
  * Some may be blank but they are provided for consistency.
  *
  * @see template_preprocess_install_page()
- *
- * @ingroup themeable
  */
 #}
   <div class="layout-container">
diff --git a/core/modules/system/templates/maintenance-page.html.twig b/core/themes/stable/templates/layout/maintenance-page.html.twig
similarity index 91%
copy from core/modules/system/templates/maintenance-page.html.twig
copy to core/themes/stable/templates/layout/maintenance-page.html.twig
index 748ed5a..de0acaa 100644
--- a/core/modules/system/templates/maintenance-page.html.twig
+++ b/core/themes/stable/templates/layout/maintenance-page.html.twig
@@ -1,14 +1,12 @@
 {#
 /**
  * @file
- * Default theme implementation to display a single Drupal page while offline.
+ * Theme override to display a single Drupal page while offline.
  *
  * All available variables are mirrored in page.html.twig.
  * Some may be blank but they are provided for consistency.
  *
  * @see template_preprocess_maintenance_page()
- *
- * @ingroup themeable
  */
 #}
 <header role="banner">
diff --git a/core/themes/classy/templates/layout/page.html.twig b/core/themes/stable/templates/layout/page.html.twig
similarity index 97%
copy from core/themes/classy/templates/layout/page.html.twig
copy to core/themes/stable/templates/layout/page.html.twig
index 16fe541..fc30edd 100644
--- a/core/themes/classy/templates/layout/page.html.twig
+++ b/core/themes/stable/templates/layout/page.html.twig
@@ -26,6 +26,7 @@
  *   slogan has been disabled in theme settings.
  *
  * Page content (in order of occurrence in the default page.html.twig):
+ * - messages: Status and error messages. Should be displayed prominently.
  * - node: Fully loaded node, if there is an automatically-loaded node
  *   associated with the page and the node ID is the second argument in the
  *   page's path (e.g. node/12345 and node/12345/revisions, but not
@@ -33,7 +34,6 @@
  *
  * Regions:
  * - page.header: Items for the header region.
- * - page.highlighted: Items for the highlighted region.
  * - page.primary_menu: Items for the primary menu region.
  * - page.secondary_menu: Items for the secondary menu region.
  * - page.highlighted: Items for the highlighted content region.
diff --git a/core/modules/system/templates/region.html.twig b/core/themes/stable/templates/layout/region.html.twig
similarity index 82%
copy from core/modules/system/templates/region.html.twig
copy to core/themes/stable/templates/layout/region.html.twig
index e009455..f34998e 100644
--- a/core/modules/system/templates/region.html.twig
+++ b/core/themes/stable/templates/layout/region.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation to display a region.
+ * Theme override to display a region.
  *
  * Available variables:
  * - content: The content for this region, typically blocks.
@@ -10,8 +10,6 @@
  *   .info.yml file.
  *
  * @see template_preprocess_region()
- *
- * @ingroup themeable
  */
 #}
 {% if content %}
diff --git a/core/modules/system/templates/feed-icon.html.twig b/core/themes/stable/templates/misc/feed-icon.html.twig
similarity index 84%
copy from core/modules/system/templates/feed-icon.html.twig
copy to core/themes/stable/templates/misc/feed-icon.html.twig
index 9b321e0..c7cb9a3 100644
--- a/core/modules/system/templates/feed-icon.html.twig
+++ b/core/themes/stable/templates/misc/feed-icon.html.twig
@@ -1,15 +1,13 @@
 {#
 /**
  * @file
- * Default theme implementation for a feed icon.
+ * Theme override for a feed icon.
  *
  * Available variables:
  * - url: An internal system path or a fully qualified external URL of the feed.
  * - attributes: Remaining HTML attributes for the feed link.
  *   - title: A descriptive title of the feed link.
  *   - class: HTML classes to be applied to the feed link.
- *
- * @ingroup themeable
  */
 #}
 <a href="{{ url }}"{{ attributes.addClass('feed-icon') }}>
diff --git a/core/themes/classy/templates/misc/progress-bar.html.twig b/core/themes/stable/templates/misc/progress-bar.html.twig
similarity index 94%
copy from core/themes/classy/templates/misc/progress-bar.html.twig
copy to core/themes/stable/templates/misc/progress-bar.html.twig
index 21a0c3c..7b67afe 100644
--- a/core/themes/classy/templates/misc/progress-bar.html.twig
+++ b/core/themes/stable/templates/misc/progress-bar.html.twig
@@ -11,7 +11,6 @@
  * - message: A string containing information to be displayed.
  */
 #}
-{{ attach_library('classy/progress') }}
 <div class="progress" data-drupal-progress>
   {% if label %}
     <div class="progress__label">{{ label }}</div>
diff --git a/core/themes/classy/templates/misc/rdf-metadata.html.twig b/core/themes/stable/templates/misc/rdf-metadata.html.twig
similarity index 90%
copy from core/themes/classy/templates/misc/rdf-metadata.html.twig
copy to core/themes/stable/templates/misc/rdf-metadata.html.twig
index acc62df..81d9172 100644
--- a/core/themes/classy/templates/misc/rdf-metadata.html.twig
+++ b/core/themes/stable/templates/misc/rdf-metadata.html.twig
@@ -16,5 +16,5 @@
  */
 #}
 {% for attributes in metadata %}
-  <span{{ attributes.addClass('rdf-meta', 'hidden') }}></span>
+  <span{{ attributes.addClass('hidden') }}></span>
 {% endfor %}
diff --git a/core/modules/rdf/templates/rdf-wrapper.html.twig b/core/themes/stable/templates/misc/rdf-wrapper.html.twig
similarity index 70%
copy from core/modules/rdf/templates/rdf-wrapper.html.twig
copy to core/themes/stable/templates/misc/rdf-wrapper.html.twig
index cfdb31e..90f50f4 100644
--- a/core/modules/rdf/templates/rdf-wrapper.html.twig
+++ b/core/themes/stable/templates/misc/rdf-wrapper.html.twig
@@ -1,13 +1,11 @@
 {#
 /**
  * @file
- * Default theme implementation for wrapping content with RDF attributes.
+ * Theme override for wrapping content with RDF attributes.
  *
  * Available variables:
  * - content: The content being wrapped with RDF attributes.
  * - attributes: HTML attributes, including RDF attributes for wrapper element.
- *
- * @ingroup themeable
  */
 #}
 <span{{ attributes }}>{{ content }}</span>
diff --git a/core/modules/system/templates/status-messages.html.twig b/core/themes/stable/templates/misc/status-messages.html.twig
similarity index 94%
copy from core/modules/system/templates/status-messages.html.twig
copy to core/themes/stable/templates/misc/status-messages.html.twig
index e479b87..f9e1eae 100644
--- a/core/modules/system/templates/status-messages.html.twig
+++ b/core/themes/stable/templates/misc/status-messages.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for status messages.
+ * Theme override for status messages.
  *
  * Displays status, error, and warning messages, grouped by type.
  *
@@ -21,8 +21,6 @@
  *   - class: HTML classes.
  *
  * @see template_preprocess_status_messages()
- *
- * @ingroup themeable
  */
 #}
 {% for type, messages in message_list %}
diff --git a/core/modules/book/templates/book-all-books-block.html.twig b/core/themes/stable/templates/navigation/book-all-books-block.html.twig
similarity index 84%
copy from core/modules/book/templates/book-all-books-block.html.twig
copy to core/themes/stable/templates/navigation/book-all-books-block.html.twig
index a4d0c9a..2eafa8e 100644
--- a/core/modules/book/templates/book-all-books-block.html.twig
+++ b/core/themes/stable/templates/navigation/book-all-books-block.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for rendering book outlines within a block.
+ * Theme override for rendering book outlines within a block.
  *
  * This template is used only when the block is configured to "show block on all
  * pages", which presents multiple independent books on all pages.
@@ -13,8 +13,6 @@
  *   - menu: The top-level book links.
  *
  * @see template_preprocess_book_all_books_block()
- *
- * @ingroup themeable
  */
 #}
 {% for book in book_menus %}
diff --git a/core/modules/book/templates/book-navigation.html.twig b/core/themes/stable/templates/navigation/book-navigation.html.twig
similarity index 96%
copy from core/modules/book/templates/book-navigation.html.twig
copy to core/themes/stable/templates/navigation/book-navigation.html.twig
index 0f12980..28a797a 100644
--- a/core/modules/book/templates/book-navigation.html.twig
+++ b/core/themes/stable/templates/navigation/book-navigation.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation to navigate books.
+ * Theme override to navigate books.
  *
  * Presented under nodes that are a part of book outlines.
  *
@@ -26,8 +26,6 @@
  * - book_title: The book/node title of the current outline being viewed.
  *
  * @see template_preprocess_book_navigation()
- *
- * @ingroup themeable
  */
 #}
 {% if tree or has_links %}
diff --git a/core/modules/book/templates/book-tree.html.twig b/core/themes/stable/templates/navigation/book-tree.html.twig
similarity index 94%
copy from core/modules/book/templates/book-tree.html.twig
copy to core/themes/stable/templates/navigation/book-tree.html.twig
index bf7424f..a012487 100644
--- a/core/modules/book/templates/book-tree.html.twig
+++ b/core/themes/stable/templates/navigation/book-tree.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation to display a book tree.
+ * Theme override to display a book tree.
  *
  * Returns HTML for a wrapper for a book sub-tree.
  *
@@ -16,8 +16,6 @@
  *   - is_collapsed: TRUE if the link has children within the current book tree
  *     that are not currently visible.
  *   - in_active_trail: TRUE if the link is in the active trail.
- *
- * @ingroup themeable
  */
 #}
 {% import _self as book_tree %}
diff --git a/core/modules/system/templates/breadcrumb.html.twig b/core/themes/stable/templates/navigation/breadcrumb.html.twig
similarity index 85%
copy from core/modules/system/templates/breadcrumb.html.twig
copy to core/themes/stable/templates/navigation/breadcrumb.html.twig
index 91d8376..7b5c6b5 100644
--- a/core/modules/system/templates/breadcrumb.html.twig
+++ b/core/themes/stable/templates/navigation/breadcrumb.html.twig
@@ -1,12 +1,10 @@
 {#
 /**
  * @file
- * Default theme implementation for a breadcrumb trail.
+ * Theme override for a breadcrumb trail.
  *
  * Available variables:
  * - breadcrumb: Breadcrumb trail items.
- *
- * @ingroup themeable
  */
 #}
 {% if breadcrumb %}
diff --git a/core/themes/classy/templates/navigation/links.html.twig b/core/themes/stable/templates/navigation/links.html.twig
similarity index 100%
copy from core/themes/classy/templates/navigation/links.html.twig
copy to core/themes/stable/templates/navigation/links.html.twig
diff --git a/core/modules/toolbar/templates/menu--toolbar.html.twig b/core/themes/stable/templates/navigation/menu--toolbar.html.twig
similarity index 95%
copy from core/modules/toolbar/templates/menu--toolbar.html.twig
copy to core/themes/stable/templates/navigation/menu--toolbar.html.twig
index 659e8f5..55cfc5b 100644
--- a/core/modules/toolbar/templates/menu--toolbar.html.twig
+++ b/core/themes/stable/templates/navigation/menu--toolbar.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation to display a toolbar menu.
+ * Theme override to display a toolbar menu.
  *
  * Available variables:
  * - menu_name: The machine name of the menu.
@@ -16,8 +16,6 @@
  *   - is_collapsed: TRUE if the link has children within the current menu tree
  *     that are not currently visible.
  *   - in_active_trail: TRUE if the link is in the active trail.
- *
- * @ingroup themeable
  */
 #}
 {% import _self as menus %}
diff --git a/core/themes/classy/templates/navigation/menu-local-action.html.twig b/core/themes/stable/templates/navigation/menu-local-action.html.twig
similarity index 100%
copy from core/themes/classy/templates/navigation/menu-local-action.html.twig
copy to core/themes/stable/templates/navigation/menu-local-action.html.twig
diff --git a/core/themes/classy/templates/navigation/menu-local-task.html.twig b/core/themes/stable/templates/navigation/menu-local-task.html.twig
similarity index 84%
copy from core/themes/classy/templates/navigation/menu-local-task.html.twig
copy to core/themes/stable/templates/navigation/menu-local-task.html.twig
index b855981..b6c3ca2 100644
--- a/core/themes/classy/templates/navigation/menu-local-task.html.twig
+++ b/core/themes/stable/templates/navigation/menu-local-task.html.twig
@@ -14,4 +14,4 @@
  * @see template_preprocess_menu_local_task()
  */
 #}
-<li{{ attributes.addClass(is_active ? 'is-active') }}>{{ link }}</li>
+<li{{ attributes }}>{{ link }}</li>
diff --git a/core/themes/classy/templates/navigation/menu-local-tasks.html.twig b/core/themes/stable/templates/navigation/menu-local-tasks.html.twig
similarity index 85%
copy from core/themes/classy/templates/navigation/menu-local-tasks.html.twig
copy to core/themes/stable/templates/navigation/menu-local-tasks.html.twig
index d3a89af..a519f23 100644
--- a/core/themes/classy/templates/navigation/menu-local-tasks.html.twig
+++ b/core/themes/stable/templates/navigation/menu-local-tasks.html.twig
@@ -15,9 +15,9 @@
 #}
 {% if primary %}
   <h2 class="visually-hidden">{{ 'Primary tabs'|t }}</h2>
-  <ul class="tabs primary">{{ primary }}</ul>
+  <ul>{{ primary }}</ul>
 {% endif %}
 {% if secondary %}
   <h2 class="visually-hidden">{{ 'Secondary tabs'|t }}</h2>
-  <ul class="tabs secondary">{{ secondary }}</ul>
+  <ul>{{ secondary }}</ul>
 {% endif %}
diff --git a/core/modules/system/templates/menu.html.twig b/core/themes/stable/templates/navigation/menu.html.twig
similarity index 94%
copy from core/modules/system/templates/menu.html.twig
copy to core/themes/stable/templates/navigation/menu.html.twig
index 03704f2..33efca8 100644
--- a/core/modules/system/templates/menu.html.twig
+++ b/core/themes/stable/templates/navigation/menu.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation to display a menu.
+ * Theme override to display a menu.
  *
  * Available variables:
  * - menu_name: The machine name of the menu.
@@ -16,8 +16,6 @@
  *   - is_collapsed: TRUE if the link has children within the current menu tree
  *     that are not currently visible.
  *   - in_active_trail: TRUE if the link is in the active trail.
- *
- * @ingroup themeable
  */
 #}
 {% import _self as menus %}
diff --git a/core/themes/classy/templates/navigation/pager.html.twig b/core/themes/stable/templates/navigation/pager.html.twig
similarity index 100%
copy from core/themes/classy/templates/navigation/pager.html.twig
copy to core/themes/stable/templates/navigation/pager.html.twig
diff --git a/core/themes/classy/templates/navigation/toolbar.html.twig b/core/themes/stable/templates/navigation/toolbar.html.twig
similarity index 95%
copy from core/themes/classy/templates/navigation/toolbar.html.twig
copy to core/themes/stable/templates/navigation/toolbar.html.twig
index 20f12d4..497bc78 100644
--- a/core/themes/classy/templates/navigation/toolbar.html.twig
+++ b/core/themes/stable/templates/navigation/toolbar.html.twig
@@ -21,7 +21,7 @@
  */
 #}
 <div{{ attributes.addClass('toolbar') }}>
-  <nav{{ toolbar_attributes.addClass('toolbar-bar', 'clearfix') }}>
+  <nav{{ toolbar_attributes.addClass('toolbar-bar') }}>
     <h2 class="visually-hidden">{{ toolbar_heading }}</h2>
     {% for key, tab in tabs %}
       {% set tray = trays[key] %}
diff --git a/core/themes/classy/templates/navigation/vertical-tabs.html.twig b/core/themes/stable/templates/navigation/vertical-tabs.html.twig
similarity index 100%
copy from core/themes/classy/templates/navigation/vertical-tabs.html.twig
copy to core/themes/stable/templates/navigation/vertical-tabs.html.twig
diff --git a/core/themes/classy/templates/user/forum-submitted.html.twig b/core/themes/stable/templates/user/forum-submitted.html.twig
similarity index 84%
copy from core/themes/classy/templates/user/forum-submitted.html.twig
copy to core/themes/stable/templates/user/forum-submitted.html.twig
index 57311e9..65680ce 100644
--- a/core/themes/classy/templates/user/forum-submitted.html.twig
+++ b/core/themes/stable/templates/user/forum-submitted.html.twig
@@ -15,7 +15,7 @@
  */
 #}
 {% if time %}
-  <span class="submitted">{% trans %}By {{ author }} {{ time }} ago{% endtrans %}</span>
+  <span>{% trans %}By {{ author }} {{ time }} ago{% endtrans %}</span>
 {% else %}
   {{ 'n/a'|t }}
 {% endif %}
diff --git a/core/themes/classy/templates/user/user.html.twig b/core/themes/stable/templates/user/user.html.twig
similarity index 93%
copy from core/themes/classy/templates/user/user.html.twig
copy to core/themes/stable/templates/user/user.html.twig
index 9a824ef..99e9472 100644
--- a/core/themes/classy/templates/user/user.html.twig
+++ b/core/themes/stable/templates/user/user.html.twig
@@ -16,7 +16,7 @@
  * @see template_preprocess_user()
  */
 #}
-<article{{ attributes.addClass('profile') }}>
+<article{{ attributes }}>
   {% if content %}
     {{- content -}}
   {% endif %}
diff --git a/core/themes/classy/templates/user/username.html.twig b/core/themes/stable/templates/user/username.html.twig
similarity index 91%
copy from core/themes/classy/templates/user/username.html.twig
copy to core/themes/stable/templates/user/username.html.twig
index 3ed5c95..828f6c6 100644
--- a/core/themes/classy/templates/user/username.html.twig
+++ b/core/themes/stable/templates/user/username.html.twig
@@ -17,7 +17,7 @@
  */
 #}
 {% if link_path -%}
-  <a{{ attributes.addClass('username') }}>{{ name }}{{ extra }}</a>
+  <a{{ attributes }}>{{ name }}{{ extra }}</a>
 {%- else -%}
   <span{{ attributes }}>{{ name }}{{ extra }}</span>
 {%- endif -%}
diff --git a/core/modules/views/templates/views-exposed-form.html.twig b/core/themes/stable/templates/views/views-exposed-form.html.twig
similarity index 81%
copy from core/modules/views/templates/views-exposed-form.html.twig
copy to core/themes/stable/templates/views/views-exposed-form.html.twig
index f8a180e..0d34594 100644
--- a/core/modules/views/templates/views-exposed-form.html.twig
+++ b/core/themes/stable/templates/views/views-exposed-form.html.twig
@@ -1,14 +1,12 @@
 {#
 /**
  * @file
- * Default theme implementation of a views exposed form.
+ * Theme override of a views exposed form.
  *
  * Available variables:
  * - form: A render element representing the form.
  *
  * @see template_preprocess_views_exposed_form()
- *
- * @ingroup themeable
  */
 #}
 {% if q is not empty %}
diff --git a/core/modules/views/templates/views-mini-pager.html.twig b/core/themes/stable/templates/views/views-mini-pager.html.twig
similarity index 94%
copy from core/modules/views/templates/views-mini-pager.html.twig
copy to core/themes/stable/templates/views/views-mini-pager.html.twig
index 2f36b16..08d794b 100644
--- a/core/modules/views/templates/views-mini-pager.html.twig
+++ b/core/themes/stable/templates/views/views-mini-pager.html.twig
@@ -1,14 +1,12 @@
 {#
 /**
  * @file
- * Default theme implementation for a views mini-pager.
+ * Theme override for a views mini-pager.
  *
  * Available variables:
  * - items: List of pager items.
  *
  * @see template_preprocess_views_mini_pager()
- *
- * @ingroup themeable
  */
 #}
 {% if items.previous or items.next %}
diff --git a/core/modules/views/templates/views-view-field.html.twig b/core/themes/stable/templates/views/views-view-field.html.twig
similarity index 87%
copy from core/modules/views/templates/views-view-field.html.twig
copy to core/themes/stable/templates/views/views-view-field.html.twig
index 04a20ac..514b121 100644
--- a/core/modules/views/templates/views-view-field.html.twig
+++ b/core/themes/stable/templates/views/views-view-field.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a single field in a view.
+ * Theme override for a single field in a view.
  *
  * Available variables:
  * - view: The view that the field belongs to.
@@ -16,8 +16,6 @@
  * of any changes in the aliasing that might happen if the view is modified.
  *
  * @see template_preprocess_views_view_field()
- *
- * @ingroup themeable
  */
 #}
 {{ output -}}
diff --git a/core/modules/views/templates/views-view-fields.html.twig b/core/themes/stable/templates/views/views-view-fields.html.twig
similarity index 95%
copy from core/modules/views/templates/views-view-fields.html.twig
copy to core/themes/stable/templates/views/views-view-fields.html.twig
index 64bd791..1370b39 100644
--- a/core/modules/views/templates/views-view-fields.html.twig
+++ b/core/themes/stable/templates/views/views-view-fields.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default view template to display all the fields in a row.
+ * Theme override to display all the fields in a row.
  *
  * Available variables:
  * - view: The view in use.
@@ -27,8 +27,6 @@
  * - row: The raw result from the query, with all data it fetched.
  *
  * @see template_preprocess_views_view_fields()
- *
- * @ingroup themeable
  */
 #}
 {% for field in fields -%}
diff --git a/core/themes/classy/templates/views/views-view-grid.html.twig b/core/themes/stable/templates/views/views-view-grid.html.twig
similarity index 100%
copy from core/themes/classy/templates/views/views-view-grid.html.twig
copy to core/themes/stable/templates/views/views-view-grid.html.twig
diff --git a/core/modules/views/templates/views-view-grouping.html.twig b/core/themes/stable/templates/views/views-view-grouping.html.twig
similarity index 80%
copy from core/modules/views/templates/views-view-grouping.html.twig
copy to core/themes/stable/templates/views/views-view-grouping.html.twig
index d786749..319607c 100644
--- a/core/modules/views/templates/views-view-grouping.html.twig
+++ b/core/themes/stable/templates/views/views-view-grouping.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation to display a single views grouping.
+ * Theme override to display a single views grouping.
  *
  * Available variables:
  * - view: The view object.
@@ -12,8 +12,6 @@
  * - rows: The rows returned from the view.
  *
  * @see template_preprocess_views_view_grouping()
- *
- * @ingroup themeable
  */
 #}
 {{ title }}
diff --git a/core/themes/classy/templates/views/views-view-list.html.twig b/core/themes/stable/templates/views/views-view-list.html.twig
similarity index 100%
copy from core/themes/classy/templates/views/views-view-list.html.twig
copy to core/themes/stable/templates/views/views-view-list.html.twig
diff --git a/core/themes/classy/templates/views/views-view-mapping-test.html.twig b/core/themes/stable/templates/views/views-view-mapping-test.html.twig
similarity index 100%
copy from core/themes/classy/templates/views/views-view-mapping-test.html.twig
copy to core/themes/stable/templates/views/views-view-mapping-test.html.twig
diff --git a/core/themes/classy/templates/views/views-view-opml.html.twig b/core/themes/stable/templates/views/views-view-opml.html.twig
similarity index 100%
copy from core/themes/classy/templates/views/views-view-opml.html.twig
copy to core/themes/stable/templates/views/views-view-opml.html.twig
diff --git a/core/themes/classy/templates/views/views-view-row-opml.html.twig b/core/themes/stable/templates/views/views-view-row-opml.html.twig
similarity index 100%
copy from core/themes/classy/templates/views/views-view-row-opml.html.twig
copy to core/themes/stable/templates/views/views-view-row-opml.html.twig
diff --git a/core/modules/views/templates/views-view-row-rss.html.twig b/core/themes/stable/templates/views/views-view-row-rss.html.twig
similarity index 86%
copy from core/modules/views/templates/views-view-row-rss.html.twig
copy to core/themes/stable/templates/views/views-view-row-rss.html.twig
index caffb33..4cdeba8 100644
--- a/core/modules/views/templates/views-view-row-rss.html.twig
+++ b/core/themes/stable/templates/views/views-view-row-rss.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation to display an item in a views RSS feed.
+ * Theme override to display an item in a views RSS feed.
  *
  * Available variables:
  * - title: RSS item title.
@@ -11,8 +11,6 @@
  *   guid).
  *
  * @see template_preprocess_views_view_row_rss()
- *
- * @ingroup themeable
  */
 #}
 <item>
diff --git a/core/themes/classy/templates/views/views-view-rss.html.twig b/core/themes/stable/templates/views/views-view-rss.html.twig
similarity index 100%
copy from core/themes/classy/templates/views/views-view-rss.html.twig
copy to core/themes/stable/templates/views/views-view-rss.html.twig
diff --git a/core/modules/views/templates/views-view-summary-unformatted.html.twig b/core/themes/stable/templates/views/views-view-summary-unformatted.html.twig
similarity index 92%
copy from core/modules/views/templates/views-view-summary-unformatted.html.twig
copy to core/themes/stable/templates/views/views-view-summary-unformatted.html.twig
index 15b955b..d9ff995 100644
--- a/core/modules/views/templates/views-view-summary-unformatted.html.twig
+++ b/core/themes/stable/templates/views/views-view-summary-unformatted.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for unformatted summary links.
+ * Theme override for unformatted summary links.
  *
  * Available variables:
  * - rows: The rows contained in this view.
@@ -16,8 +16,6 @@
  *     or block level HTML element.
  *
  * @see template_preprocess_views_view_summary_unformatted()
- *
- * @ingroup themeable
  */
 #}
 {% for row in rows  %}
diff --git a/core/themes/classy/templates/views/views-view-summary.html.twig b/core/themes/stable/templates/views/views-view-summary.html.twig
similarity index 92%
copy from core/themes/classy/templates/views/views-view-summary.html.twig
copy to core/themes/stable/templates/views/views-view-summary.html.twig
index 241aa50..d12ba23 100644
--- a/core/themes/classy/templates/views/views-view-summary.html.twig
+++ b/core/themes/stable/templates/views/views-view-summary.html.twig
@@ -18,8 +18,7 @@
  * @see template_preprocess_views_view_summary()
  */
 #}
-<div class="item-list">
-  <ul class="views-summary">
+<ul>
   {% for row in rows %}
     <li><a href="{{ row.url }}"{{ row.attributes.addClass(row.active ? 'is-active')|without('href') }}>{{ row.link }}</a>
       {% if options.count %}
@@ -27,5 +26,4 @@
       {% endif %}
     </li>
   {% endfor %}
-  </ul>
-</div>
+</ul>
diff --git a/core/themes/classy/templates/views/views-view-table.html.twig b/core/themes/stable/templates/views/views-view-table.html.twig
similarity index 99%
copy from core/themes/classy/templates/views/views-view-table.html.twig
copy to core/themes/stable/templates/views/views-view-table.html.twig
index 8eccec0..6806eb5 100644
--- a/core/themes/classy/templates/views/views-view-table.html.twig
+++ b/core/themes/stable/templates/views/views-view-table.html.twig
@@ -32,8 +32,6 @@
 #}
 {%
   set classes = [
-    'views-table',
-    'views-view-table',
     'cols-' ~ header|length,
     responsive ? 'responsive-enabled',
     sticky ? 'sticky-enabled',
diff --git a/core/themes/classy/templates/views/views-view-unformatted.html.twig b/core/themes/stable/templates/views/views-view-unformatted.html.twig
similarity index 100%
copy from core/themes/classy/templates/views/views-view-unformatted.html.twig
copy to core/themes/stable/templates/views/views-view-unformatted.html.twig
diff --git a/core/modules/views/templates/views-view.html.twig b/core/themes/stable/templates/views/views-view.html.twig
similarity index 95%
copy from core/modules/views/templates/views-view.html.twig
copy to core/themes/stable/templates/views/views-view.html.twig
index e81b1ab..5d372d7 100644
--- a/core/modules/views/templates/views-view.html.twig
+++ b/core/themes/stable/templates/views/views-view.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for main view template.
+ * Theme override for main view template.
  *
  * Available variables:
  * - attributes: Remaining HTML attributes for the element.
@@ -28,8 +28,6 @@
  *   Javascript.
  *
  * @see template_preprocess_views_view()
- *
- * @ingroup themeable
  */
 #}
 {%