diff --git a/core/modules/block/block.admin.inc b/core/modules/block/block.admin.inc
index f94ce25..faa72c9 100644
--- a/core/modules/block/block.admin.inc
+++ b/core/modules/block/block.admin.inc
@@ -13,7 +13,7 @@
  * @see block_menu()
  */
 function block_admin_demo($theme = NULL) {
-  drupal_add_css(drupal_get_path('module', 'block') . '/block.admin.css');
+  drupal_add_css(drupal_get_path('module', 'block') . '/css/block.admin.css');
   return '';
 }
 
diff --git a/core/modules/block/block.admin.css b/core/modules/block/css/block.admin.css
similarity index 100%
rename from core/modules/block/block.admin.css
rename to core/modules/block/css/block.admin.css
diff --git a/core/modules/block/lib/Drupal/block/BlockListController.php b/core/modules/block/lib/Drupal/block/BlockListController.php
index 5b18b3c..b36c67a 100644
--- a/core/modules/block/lib/Drupal/block/BlockListController.php
+++ b/core/modules/block/lib/Drupal/block/BlockListController.php
@@ -106,7 +106,7 @@ public function getFormID() {
    */
   public function buildForm(array $form, array &$form_state) {
     $entities = $this->load();
-    $form['#attached']['css'][] = drupal_get_path('module', 'block') . '/block.admin.css';
+    $form['#attached']['css'][] = drupal_get_path('module', 'block') . '/css/block.admin.css';
     $form['#attached']['library'][] = array('system', 'drupal.tableheader');
     $form['#attached']['library'][] = array('block', 'drupal.block');
 
diff --git a/core/modules/color/color.module b/core/modules/color/color.module
index 2203133..6942c6f 100644
--- a/core/modules/color/color.module
+++ b/core/modules/color/color.module
@@ -194,7 +194,7 @@ function color_scheme_form($complete_form, &$form_state, $theme) {
       ),
       // Add custom CSS.
       'css' => array(
-        $base . '/color.admin.css' => array(),
+        $base . '/css/color.admin.css' => array(),
       ),
       // Add custom JavaScript.
       'js' => array(
diff --git a/core/modules/color/color.admin-rtl.css b/core/modules/color/css/color.admin-rtl.css
similarity index 100%
rename from core/modules/color/color.admin-rtl.css
rename to core/modules/color/css/color.admin-rtl.css
diff --git a/core/modules/color/color.admin.css b/core/modules/color/css/color.admin.css
similarity index 100%
rename from core/modules/color/color.admin.css
rename to core/modules/color/css/color.admin.css
diff --git a/core/modules/entity_reference/css/entity_reference-rtl.admin.css b/core/modules/entity_reference/css/entity_reference.admin-rtl.css
similarity index 100%
rename from core/modules/entity_reference/css/entity_reference-rtl.admin.css
rename to core/modules/entity_reference/css/entity_reference.admin-rtl.css
diff --git a/core/modules/field_ui/field_ui.admin-rtl.css b/core/modules/field_ui/css/field_ui.admin-rtl.css
similarity index 100%
rename from core/modules/field_ui/field_ui.admin-rtl.css
rename to core/modules/field_ui/css/field_ui.admin-rtl.css
diff --git a/core/modules/field_ui/field_ui.admin.css b/core/modules/field_ui/css/field_ui.admin.css
similarity index 100%
rename from core/modules/field_ui/field_ui.admin.css
rename to core/modules/field_ui/css/field_ui.admin.css
diff --git a/core/modules/field_ui/field_ui.module b/core/modules/field_ui/field_ui.module
index 88d2ce7..865660b 100644
--- a/core/modules/field_ui/field_ui.module
+++ b/core/modules/field_ui/field_ui.module
@@ -335,7 +335,7 @@ function field_ui_library_info() {
       drupal_get_path('module', 'field_ui') . '/field_ui.js' => array(),
     ),
     'css' => array(
-      drupal_get_path('module', 'field_ui') . '/field_ui.admin.css' => array(),
+      drupal_get_path('module', 'field_ui') . '/css/field_ui.admin.css' => array(),
     ),
     'dependencies' => array(
       array('system', 'jquery'),
diff --git a/core/modules/file/file.admin.css b/core/modules/file/css/file.admin.css
similarity index 100%
rename from core/modules/file/file.admin.css
rename to core/modules/file/css/file.admin.css
diff --git a/core/modules/file/file.module b/core/modules/file/file.module
index 79b63ef..afc8f4e 100644
--- a/core/modules/file/file.module
+++ b/core/modules/file/file.module
@@ -1658,7 +1658,7 @@ function file_library_info() {
       drupal_get_path('module', 'file') . '/file.js' => array(),
     ),
     'css' => array(
-      drupal_get_path('module', 'file') . '/file.admin.css'
+      drupal_get_path('module', 'file') . '/css/file.admin.css'
     ),
     'dependencies' => array(
       array('system', 'jquery'),
diff --git a/core/modules/filter/filter.admin-rtl.css b/core/modules/filter/css/filter.admin-rtl.css
similarity index 100%
rename from core/modules/filter/filter.admin-rtl.css
rename to core/modules/filter/css/filter.admin-rtl.css
diff --git a/core/modules/filter/filter.admin.css b/core/modules/filter/css/filter.admin.css
similarity index 100%
rename from core/modules/filter/filter.admin.css
rename to core/modules/filter/css/filter.admin.css
diff --git a/core/modules/filter/filter.module b/core/modules/filter/filter.module
index 57ff8c2..93cb8af 100644
--- a/core/modules/filter/filter.module
+++ b/core/modules/filter/filter.module
@@ -1811,7 +1811,7 @@ function filter_library_info() {
       drupal_get_path('module', 'filter') . '/filter.admin.js' => array(),
     ),
     'css' => array(
-      drupal_get_path('module', 'filter') . '/filter.admin.css'
+      drupal_get_path('module', 'filter') . '/css/filter.admin.css'
     ),
     'dependencies' => array(
       array('system', 'jquery'),
@@ -1827,7 +1827,7 @@ function filter_library_info() {
       drupal_get_path('module', 'filter') . '/filter.js' => array(),
     ),
     'css' => array(
-      drupal_get_path('module', 'filter') . '/filter.admin.css'
+      drupal_get_path('module', 'filter') . '/css/filter.admin.css'
     ),
     'dependencies' => array(
       array('system', 'jquery'),
diff --git a/core/modules/help/css/help-rtl.css b/core/modules/help/css/help.module-rtl.css
similarity index 100%
rename from core/modules/help/css/help-rtl.css
rename to core/modules/help/css/help.module-rtl.css
diff --git a/core/modules/help/lib/Drupal/help/Controller/HelpController.php b/core/modules/help/lib/Drupal/help/Controller/HelpController.php
index 118f1bc..9533a45 100644
--- a/core/modules/help/lib/Drupal/help/Controller/HelpController.php
+++ b/core/modules/help/lib/Drupal/help/Controller/HelpController.php
@@ -47,7 +47,7 @@ public static function create(ContainerInterface $container) {
    */
   public function helpMain() {
     // Add CSS.
-    drupal_add_css(drupal_get_path('module', 'help') . '/help.css');
+    drupal_add_css(drupal_get_path('module', 'help') . '/css/help.module.css');
     $output = '<h2>' . t('Help topics') . '</h2><p>' . t('Help is available on the following items:') . '</p>' . $this->helpLinksAsList();
     return $output;
   }
diff --git a/core/modules/help/lib/Drupal/help/Tests/HelpTest.php b/core/modules/help/lib/Drupal/help/Tests/HelpTest.php
index 54b955f..5a40fa0 100644
--- a/core/modules/help/lib/Drupal/help/Tests/HelpTest.php
+++ b/core/modules/help/lib/Drupal/help/Tests/HelpTest.php
@@ -67,7 +67,7 @@ public function testHelp() {
     // Check for css on admin/help.
     $this->drupalLogin($this->adminUser);
     $this->drupalGet('admin/help');
-    $this->assertRaw(drupal_get_path('module', 'help') . '/help.css', 'The help.css file is present in the HTML.');
+    $this->assertRaw(drupal_get_path('module', 'help') . '/css/help.module.css', 'The help.module.css file is present in the HTML.');
 
     // Verify that introductory help text exists, goes for 100% module coverage.
     $this->assertRaw(t('For more information, refer to the specific topics listed in the next section or to the <a href="@drupal">online Drupal handbooks</a>.', array('@drupal' => 'http://drupal.org/documentation')), 'Help intro text correctly appears.');
diff --git a/core/modules/language/language.admin.css b/core/modules/language/css/language.admin.css
similarity index 100%
rename from core/modules/language/language.admin.css
rename to core/modules/language/css/language.admin.css
diff --git a/core/modules/language/language.admin.inc b/core/modules/language/language.admin.inc
index 59f1efa..ac74215 100644
--- a/core/modules/language/language.admin.inc
+++ b/core/modules/language/language.admin.inc
@@ -805,7 +805,7 @@ function language_content_settings_form(array $form, array $form_state, array $s
   $form = array(
     '#labels' => $labels,
     '#attached' => array(
-      'css' => array($path . '/language.admin.css'),
+      'css' => array($path . '/css/language.admin.css'),
     ),
   );
 
diff --git a/core/modules/layout/layout.admin.css b/core/modules/layout/css/layout.admin.css
similarity index 100%
rename from core/modules/layout/layout.admin.css
rename to core/modules/layout/css/layout.admin.css
diff --git a/core/modules/layout/layout.admin.inc b/core/modules/layout/layout.admin.inc
index 797c4c7..fac4370 100644
--- a/core/modules/layout/layout.admin.inc
+++ b/core/modules/layout/layout.admin.inc
@@ -30,6 +30,6 @@ function layout_page_view($key) {
     '#type' => 'markup',
     '#markup' => $instance->renderLayout(TRUE, $regions),
   );
-  $build['#attached']['css'][] = drupal_get_path('module', 'layout') . '/layout.admin.css';
+  $build['#attached']['css'][] = drupal_get_path('module', 'layout') . '/css/layout.admin.css';
   return $build;
 }
diff --git a/core/modules/locale/locale.admin-rtl.css b/core/modules/locale/css/locale.admin-rtl.css
similarity index 100%
rename from core/modules/locale/locale.admin-rtl.css
rename to core/modules/locale/css/locale.admin-rtl.css
diff --git a/core/modules/locale/locale.admin.css b/core/modules/locale/css/locale.admin.css
similarity index 100%
rename from core/modules/locale/locale.admin.css
rename to core/modules/locale/css/locale.admin.css
diff --git a/core/modules/locale/locale.pages.inc b/core/modules/locale/locale.pages.inc
index a109f5f..dfb841b 100644
--- a/core/modules/locale/locale.pages.inc
+++ b/core/modules/locale/locale.pages.inc
@@ -163,7 +163,7 @@ function locale_translate_filter_form($form, &$form_state) {
   $filter_values = locale_translate_filter_values();
 
   $form['#attached']['css'] = array(
-    drupal_get_path('module', 'locale') . '/locale.admin.css',
+    drupal_get_path('module', 'locale') . '/css/locale.admin.css',
   );
 
   $form['filters'] = array(
@@ -260,7 +260,7 @@ function locale_translate_edit_form($form, &$form_state) {
 
   $path = drupal_get_path('module', 'locale');
   $form['#attached']['css'] = array(
-    $path . '/locale.admin.css',
+    $path . '/css/locale.admin.css',
   );
   $form['#attached']['library'][] = array('locale', 'drupal.locale.admin');
 
@@ -583,7 +583,7 @@ function locale_translation_status_form($form, &$form_state) {
   );
 
   $form['#attached']['library'][] = array('locale', 'drupal.locale.admin');
-  $form['#attached']['css'] = array(drupal_get_path('module', 'locale') . '/locale.admin.css');
+  $form['#attached']['css'] = array(drupal_get_path('module', 'locale') . '/css/locale.admin.css');
 
   $form['actions'] = array('#type' => 'actions');
   if ($languages_update) {
diff --git a/core/modules/menu/menu.admin.css b/core/modules/menu/css/menu.admin.css
similarity index 100%
rename from core/modules/menu/menu.admin.css
rename to core/modules/menu/css/menu.admin.css
diff --git a/core/modules/menu/lib/Drupal/menu/MenuListController.php b/core/modules/menu/lib/Drupal/menu/MenuListController.php
index e557d92..1ed2200 100644
--- a/core/modules/menu/lib/Drupal/menu/MenuListController.php
+++ b/core/modules/menu/lib/Drupal/menu/MenuListController.php
@@ -71,7 +71,7 @@ public function getOperations(EntityInterface $entity) {
    */
   public function render() {
     $build = parent::render();
-    $build['#attached']['css'][] = drupal_get_path('module', 'menu') . '/menu.admin.css';
+    $build['#attached']['css'][] = drupal_get_path('module', 'menu') . '/css/menu.admin.css';
     return $build;
   }
 
diff --git a/core/modules/menu/menu.admin.inc b/core/modules/menu/menu.admin.inc
index 4150b99..f08ddbd 100644
--- a/core/modules/menu/menu.admin.inc
+++ b/core/modules/menu/menu.admin.inc
@@ -71,7 +71,7 @@ function menu_overview_form($form, &$form_state) {
   $form['#theme'] = 'menu_overview_form';
   $form_state += array('menu_overview_form_parents' => array());
 
-  $form['#attached']['css'] = array(drupal_get_path('module', 'menu') . '/menu.admin.css');
+  $form['#attached']['css'] = array(drupal_get_path('module', 'menu') . '/css/menu.admin.css');
 
   $links = array();
   $query = Drupal::entityQuery('menu_link')
diff --git a/core/modules/translation_entity/translation_entity.admin.css b/core/modules/translation_entity/css/translation_entity.admin.css
similarity index 100%
rename from core/modules/translation_entity/translation_entity.admin.css
rename to core/modules/translation_entity/css/translation_entity.admin.css
diff --git a/core/modules/translation_entity/translation_entity.module b/core/modules/translation_entity/translation_entity.module
index 82bd66d..6ce4ecf 100644
--- a/core/modules/translation_entity/translation_entity.module
+++ b/core/modules/translation_entity/translation_entity.module
@@ -362,7 +362,7 @@ function translation_entity_library_info() {
       $path . '/translation_entity.admin.js' => array(),
     ),
     'css' => array(
-      $path . '/translation_entity.admin.css' => array(),
+      $path . '/css/translation_entity.admin.css' => array(),
     ),
     'dependencies' => array(
       array('system', 'jquery'),
diff --git a/core/modules/update/update-rtl.css b/core/modules/update/css/update.admin-rtl.css
similarity index 100%
rename from core/modules/update/update-rtl.css
rename to core/modules/update/css/update.admin-rtl.css
diff --git a/core/modules/update/update.css b/core/modules/update/css/update.admin.css
similarity index 100%
rename from core/modules/update/update.css
rename to core/modules/update/css/update.admin.css
diff --git a/core/modules/update/update.manager.inc b/core/modules/update/update.manager.inc
index bc84058..26cd673 100644
--- a/core/modules/update/update.manager.inc
+++ b/core/modules/update/update.manager.inc
@@ -77,7 +77,7 @@ function update_manager_update_form($form, $form_state = array(), $context) {
     return $form;
   }
 
-  $form['#attached']['css'][] = drupal_get_path('module', 'update') . '/update.css';
+  $form['#attached']['css'][] = drupal_get_path('module', 'update') . '/css/update.admin.css';
 
   // This will be a nested array. The first key is the kind of project, which
   // can be either 'enabled', 'disabled', 'manual' (projects which require
diff --git a/core/modules/update/update.report.inc b/core/modules/update/update.report.inc
index 35677d8..afb0a5c 100644
--- a/core/modules/update/update.report.inc
+++ b/core/modules/update/update.report.inc
@@ -231,7 +231,7 @@ function theme_update_report($variables) {
       $output .= theme('table', array('header' => $header, 'rows' => $rows[$type_name], 'attributes' => array('class' => array('update'))));
     }
   }
-  drupal_add_css(drupal_get_path('module', 'update') . '/update.css');
+  drupal_add_css(drupal_get_path('module', 'update') . '/css/update.admin.css');
   return $output;
 }
 
