diff --git a/core/lib/Drupal/Core/Extension/ThemeHandler.php b/core/lib/Drupal/Core/Extension/ThemeHandler.php
index d9ef77e..971bd20 100644
--- a/core/lib/Drupal/Core/Extension/ThemeHandler.php
+++ b/core/lib/Drupal/Core/Extension/ThemeHandler.php
@@ -376,18 +376,7 @@ public function listInfo() {
    * {@inheritdoc}
    */
   public function addTheme(Extension $theme) {
-    // @todo Remove this 100% unnecessary duplication of properties.
-    foreach ($theme->info['stylesheets'] as $media => $stylesheets) {
-      foreach ($stylesheets as $stylesheet => $path) {
-        $theme->stylesheets[$media][$stylesheet] = $path;
-      }
-    }
-    foreach ($theme->info['libraries'] as $library => $name) {
-      $theme->libraries[$library] = $name;
-    }
-    if (isset($theme->info['engine'])) {
-      $theme->engine = $theme->info['engine'];
-    }
+    // @todo We
     if (isset($theme->info['base theme'])) {
       $theme->base_theme = $theme->info['base theme'];
     }
diff --git a/core/lib/Drupal/Core/Theme/ThemeInitialization.php b/core/lib/Drupal/Core/Theme/ThemeInitialization.php
index c6d800e..40f758a 100644
--- a/core/lib/Drupal/Core/Theme/ThemeInitialization.php
+++ b/core/lib/Drupal/Core/Theme/ThemeInitialization.php
@@ -153,8 +153,8 @@ public function getActiveTheme(Extension $theme, array $base_themes = []) {
     // Grab stylesheets from base theme.
     $final_stylesheets = array();
     foreach ($base_themes as $base) {
-      if (!empty($base->stylesheets)) {
-        foreach ($base->stylesheets as $media => $stylesheets) {
+      if (!empty($base->info['stylesheets'])) {
+        foreach ($base->info['stylesheets'] as $media => $stylesheets) {
           foreach ($stylesheets as $name => $stylesheet) {
             $final_stylesheets[$media][$name] = $stylesheet;
           }
@@ -175,8 +175,8 @@ public function getActiveTheme(Extension $theme, array $base_themes = []) {
     }
 
     // Add stylesheets used by this theme.
-    if (!empty($theme->stylesheets)) {
-      foreach ($theme->stylesheets as $media => $stylesheets) {
+    if (!empty($theme->info['stylesheets'])) {
+      foreach ($theme->info['stylesheets'] as $media => $stylesheets) {
         foreach ($stylesheets as $name => $stylesheet) {
           $final_stylesheets[$media][$name] = $stylesheet;
         }
@@ -210,21 +210,21 @@ public function getActiveTheme(Extension $theme, array $base_themes = []) {
 
     // Grab libraries from base theme
     foreach ($base_themes as $base) {
-      if (!empty($base->libraries)) {
-        foreach ($base->libraries as $library) {
+      if (!empty($base->info['libraries'])) {
+        foreach ($base->info['libraries'] as $library) {
           $values['libraries'][] = $library;
         }
       }
     }
 
     // Add libraries used by this theme.
-    if (!empty($theme->libraries)) {
-      foreach ($theme->libraries as $library) {
+    if (!empty($theme->info['libraries'])) {
+      foreach ($theme->info['libraries'] as $library) {
         $values['libraries'][] = $library;
       }
     }
 
-    $values['engine'] = isset($theme->engine) ? $theme->engine : NULL;
+    $values['engine'] = isset($theme->info['engine']) ? $theme->info['engine'] : NULL;
     $values['owner'] = isset($theme->owner) ? $theme->owner : NULL;
     $values['extension'] = $theme;
 
diff --git a/core/modules/color/color.module b/core/modules/color/color.module
index 7010ddf..a7497b8 100644
--- a/core/modules/color/color.module
+++ b/core/modules/color/color.module
@@ -68,15 +68,15 @@ function color_form_system_theme_settings_alter(&$form, FormStateInterface $form
  * Replaces style sheets with color-altered style sheets.
  */
 function color_css_alter(&$css) {
-  $theme_key = \Drupal::theme()->getActiveTheme()->getName();
-  $themes = list_themes();
+  $active_theme = \Drupal::theme()->getActiveTheme();
+  $theme_name = $active_theme->getName();
 
   // Override stylesheets.
-  $color_paths = \Drupal::config('color.theme.' . $theme_key)->get('stylesheets');
+  $color_paths = \Drupal::config('color.theme.' . $theme_name)->get('stylesheets');
 
-  if (!empty($color_paths) && !empty($themes[$theme_key]->stylesheets['all'])) {
+  if (!empty($color_paths) && $active_theme->getStyleSheets()['all']) {
 
-    foreach ($themes[$theme_key]->stylesheets['all'] as $old_path) {
+    foreach ($active_theme->getStyleSheets()['all'] as $old_path) {
       // Loop over the path array with recolored CSS files to find matching
       // paths which could replace the non-recolored paths.
       foreach ($color_paths as $color_path) {
diff --git a/core/modules/system/src/Tests/Extension/ThemeHandlerTest.php b/core/modules/system/src/Tests/Extension/ThemeHandlerTest.php
index f652bfd..fa6d984 100644
--- a/core/modules/system/src/Tests/Extension/ThemeHandlerTest.php
+++ b/core/modules/system/src/Tests/Extension/ThemeHandlerTest.php
@@ -8,6 +8,7 @@
 namespace Drupal\system\Tests\Extension;
 
 use Drupal\Core\DependencyInjection\ContainerBuilder;
+use Drupal\Core\Extension\ExtensionDiscovery;
 use Drupal\Core\Extension\ExtensionNameLengthException;
 use Drupal\simpletest\DrupalUnitTestBase;
 
diff --git a/core/modules/system/src/Tests/Theme/ThemeTest.php b/core/modules/system/src/Tests/Theme/ThemeTest.php
index 5195163..c28997b 100644
--- a/core/modules/system/src/Tests/Theme/ThemeTest.php
+++ b/core/modules/system/src/Tests/Theme/ThemeTest.php
@@ -210,8 +210,6 @@ function testListThemes() {
     $sub_theme_list = array('test_subtheme' => 'Theme test subtheme');
     $this->assertIdentical($themes['test_basetheme']->sub_themes, $sub_theme_list, 'Base theme\'s object includes list of subthemes.');
     $this->assertIdentical($themes['test_subtheme']->base_themes, $base_theme_list, 'Subtheme\'s object includes list of base themes.');
-    // Check for theme engine in subtheme.
-    $this->assertIdentical($themes['test_subtheme']->engine, 'twig', 'Subtheme\'s object includes the theme engine.');
     // Check for theme engine prefix.
     $this->assertIdentical($themes['test_basetheme']->prefix, 'twig', 'Base theme\'s object includes the theme engine prefix.');
     $this->assertIdentical($themes['test_subtheme']->prefix, 'twig', 'Subtheme\'s object includes the theme engine prefix.');