diff --git a/core/modules/ckeditor/src/Plugin/Editor/CKEditor.php b/core/modules/ckeditor/src/Plugin/Editor/CKEditor.php
index 914c1b4..62aac38 100644
--- a/core/modules/ckeditor/src/Plugin/Editor/CKEditor.php
+++ b/core/modules/ckeditor/src/Plugin/Editor/CKEditor.php
@@ -416,7 +416,7 @@ public function buildToolbarJSSetting(EditorEntity $editor) {
   public function buildContentsCssJSSetting(EditorEntity $editor) {
     $css = array(
       drupal_get_path('module', 'ckeditor') . '/css/ckeditor-iframe.css',
-      drupal_get_path('module', 'system') . '/css/components/align.module.css',
+      drupal_get_path('module', 'system') . '/css/components/align.css',
     );
     $this->moduleHandler->alter('ckeditor_css', $css, $editor);
     $css = array_merge($css, _ckeditor_theme_css());
diff --git a/core/modules/ckeditor/src/Tests/CKEditorTest.php b/core/modules/ckeditor/src/Tests/CKEditorTest.php
index d2a59bc..6655a64 100644
--- a/core/modules/ckeditor/src/Tests/CKEditorTest.php
+++ b/core/modules/ckeditor/src/Tests/CKEditorTest.php
@@ -468,7 +468,7 @@ protected function getDefaultToolbarConfig() {
   protected function getDefaultContentsCssConfig() {
     return array(
       file_create_url('core/modules/ckeditor/css/ckeditor-iframe.css'),
-      file_create_url('core/modules/system/css/components/align.module.css'),
+      file_create_url('core/modules/system/css/components/align.css'),
     );
   }
 
diff --git a/core/modules/contextual/contextual.libraries.yml b/core/modules/contextual/contextual.libraries.yml
index 51281af..007ffd8 100644
--- a/core/modules/contextual/contextual.libraries.yml
+++ b/core/modules/contextual/contextual.libraries.yml
@@ -13,7 +13,7 @@ drupal.contextual-links:
     js/views/VisualView.js: { weight: -2 }
   css:
     component:
-      css/contextual.module.css: {}
+      css/contextual.css: {}
     theme:
       css/contextual.theme.css: {}
       css/contextual.icons.theme.css: {}
diff --git a/core/modules/contextual/css/contextual.module.css b/core/modules/contextual/css/contextual.css
similarity index 100%
rename from core/modules/contextual/css/contextual.module.css
rename to core/modules/contextual/css/contextual.css
diff --git a/core/modules/dblog/css/dblog.module.css b/core/modules/dblog/css/dblog.css
similarity index 100%
rename from core/modules/dblog/css/dblog.module.css
rename to core/modules/dblog/css/dblog.css
diff --git a/core/modules/dblog/dblog.libraries.yml b/core/modules/dblog/dblog.libraries.yml
index d871d09..8b49aec 100644
--- a/core/modules/dblog/dblog.libraries.yml
+++ b/core/modules/dblog/dblog.libraries.yml
@@ -2,4 +2,4 @@ drupal.dblog:
   version: VERSION
   css:
     component:
-      css/dblog.module.css: {}
+      css/dblog.css: {}
diff --git a/core/modules/node/css/node.module.css b/core/modules/node/css/node.css
similarity index 100%
rename from core/modules/node/css/node.module.css
rename to core/modules/node/css/node.css
diff --git a/core/modules/node/node.libraries.yml b/core/modules/node/node.libraries.yml
index 22c93ac..fac3736 100644
--- a/core/modules/node/node.libraries.yml
+++ b/core/modules/node/node.libraries.yml
@@ -2,7 +2,7 @@ drupal.node:
   version: VERSION
   css:
     layout:
-      css/node.module.css: {}
+      css/node.css: {}
   js:
     node.js: {}
   dependencies:
@@ -37,7 +37,7 @@ form:
   version: VERSION
   css:
     layout:
-      css/node.module.css: {}
+      css/node.css: {}
 
 drupal.node.admin:
   version: VERSION
diff --git a/core/modules/quickedit/css/quickedit.module.css b/core/modules/quickedit/css/quickedit.css
similarity index 100%
rename from core/modules/quickedit/css/quickedit.module.css
rename to core/modules/quickedit/css/quickedit.css
diff --git a/core/modules/quickedit/quickedit.libraries.yml b/core/modules/quickedit/quickedit.libraries.yml
index 7c81563..f87eb3b 100644
--- a/core/modules/quickedit/quickedit.libraries.yml
+++ b/core/modules/quickedit/quickedit.libraries.yml
@@ -22,7 +22,7 @@ quickedit:
     js/theme.js: {}
   css:
     component:
-      css/quickedit.module.css: {}
+      css/quickedit.css: {}
     theme:
       css/quickedit.theme.css: {}
       css/quickedit.icons.theme.css: {}
diff --git a/core/modules/simpletest/css/simpletest.module.css b/core/modules/simpletest/css/simpletest.css
similarity index 100%
rename from core/modules/simpletest/css/simpletest.module.css
rename to core/modules/simpletest/css/simpletest.css
diff --git a/core/modules/simpletest/simpletest.libraries.yml b/core/modules/simpletest/simpletest.libraries.yml
index 7bcbc07..c6162e8 100644
--- a/core/modules/simpletest/simpletest.libraries.yml
+++ b/core/modules/simpletest/simpletest.libraries.yml
@@ -4,7 +4,7 @@ drupal.simpletest:
     simpletest.js: {}
   css:
     component:
-      css/simpletest.module.css: {}
+      css/simpletest.css: {}
   dependencies:
     - core/jquery
     - core/drupal
diff --git a/core/modules/system/css/components/ajax-progress.module.css b/core/modules/system/css/components/ajax-progress.css
similarity index 100%
rename from core/modules/system/css/components/ajax-progress.module.css
rename to core/modules/system/css/components/ajax-progress.css
diff --git a/core/modules/system/css/components/align.module.css b/core/modules/system/css/components/align.css
similarity index 100%
rename from core/modules/system/css/components/align.module.css
rename to core/modules/system/css/components/align.css
diff --git a/core/modules/system/css/components/autocomplete-loading.module.css b/core/modules/system/css/components/autocomplete-loading.css
similarity index 100%
rename from core/modules/system/css/components/autocomplete-loading.module.css
rename to core/modules/system/css/components/autocomplete-loading.css
diff --git a/core/modules/system/css/components/clearfix.module.css b/core/modules/system/css/components/clearfix.css
similarity index 100%
rename from core/modules/system/css/components/clearfix.module.css
rename to core/modules/system/css/components/clearfix.css
diff --git a/core/modules/system/css/components/container-inline.module.css b/core/modules/system/css/components/container-inline.css
similarity index 100%
rename from core/modules/system/css/components/container-inline.module.css
rename to core/modules/system/css/components/container-inline.css
diff --git a/core/modules/system/css/components/details.module.css b/core/modules/system/css/components/details.css
similarity index 100%
rename from core/modules/system/css/components/details.module.css
rename to core/modules/system/css/components/details.css
diff --git a/core/modules/system/css/components/fieldgroup.module.css b/core/modules/system/css/components/fieldgroup.css
similarity index 100%
rename from core/modules/system/css/components/fieldgroup.module.css
rename to core/modules/system/css/components/fieldgroup.css
diff --git a/core/modules/system/css/components/hidden.module.css b/core/modules/system/css/components/hidden.css
similarity index 100%
rename from core/modules/system/css/components/hidden.module.css
rename to core/modules/system/css/components/hidden.css
diff --git a/core/modules/system/css/components/js.module.css b/core/modules/system/css/components/js.css
similarity index 100%
rename from core/modules/system/css/components/js.module.css
rename to core/modules/system/css/components/js.css
diff --git a/core/modules/system/css/components/nowrap.module.css b/core/modules/system/css/components/nowrap.css
similarity index 100%
rename from core/modules/system/css/components/nowrap.module.css
rename to core/modules/system/css/components/nowrap.css
diff --git a/core/modules/system/css/components/position-container.module.css b/core/modules/system/css/components/position-container.css
similarity index 100%
rename from core/modules/system/css/components/position-container.module.css
rename to core/modules/system/css/components/position-container.css
diff --git a/core/modules/system/css/components/progress.module.css b/core/modules/system/css/components/progress.css
similarity index 100%
rename from core/modules/system/css/components/progress.module.css
rename to core/modules/system/css/components/progress.css
diff --git a/core/modules/system/css/components/reset-appearance.module.css b/core/modules/system/css/components/reset-appearance.css
similarity index 100%
rename from core/modules/system/css/components/reset-appearance.module.css
rename to core/modules/system/css/components/reset-appearance.css
diff --git a/core/modules/system/css/components/resize.module.css b/core/modules/system/css/components/resize.css
similarity index 100%
rename from core/modules/system/css/components/resize.module.css
rename to core/modules/system/css/components/resize.css
diff --git a/core/modules/system/css/components/sticky-header.module.css b/core/modules/system/css/components/sticky-header.css
similarity index 100%
rename from core/modules/system/css/components/sticky-header.module.css
rename to core/modules/system/css/components/sticky-header.css
diff --git a/core/modules/system/css/components/tabledrag.module.css b/core/modules/system/css/components/tabledrag.css
similarity index 100%
rename from core/modules/system/css/components/tabledrag.module.css
rename to core/modules/system/css/components/tabledrag.css
diff --git a/core/modules/system/css/components/tree-child.module.css b/core/modules/system/css/components/tree-child.css
similarity index 100%
rename from core/modules/system/css/components/tree-child.module.css
rename to core/modules/system/css/components/tree-child.css
diff --git a/core/modules/system/system.libraries.yml b/core/modules/system/system.libraries.yml
index 9493f52..61e86ec 100644
--- a/core/modules/system/system.libraries.yml
+++ b/core/modules/system/system.libraries.yml
@@ -3,22 +3,23 @@ base:
   css:
     # Adjust the weights to load these early.
     component:
-      css/components/ajax-progress.module.css: { weight: -10 }
-      css/components/align.module.css: { weight: -10 }
-      css/components/autocomplete-loading.module.css: { weight: -10 }
-      css/components/fieldgroup.module.css: { weight: -10 }
-      css/components/container-inline.module.css: { weight: -10 }
-      css/components/clearfix.module.css: { weight: -10 }
-      css/components/details.module.css: { weight: -10 }
-      css/components/hidden.module.css: { weight: -10 }
-      css/components/js.module.css: { weight: -10 }
-      css/components/nowrap.module.css: { weight: -10 }
-      css/components/position-container.module.css: { weight: -10 }
-      css/components/progress.module.css: { weight: -10 }
-      css/components/reset-appearance.module.css: { weight: -10 }
-      css/components/resize.module.css: { weight: -10 }
-      css/components/sticky-header.module.css: { weight: -10 }
-      css/components/tabledrag.module.css: { weight: -10 }
+      css/components/ajax-progress.css: { weight: -10 }
+      css/components/align.css: { weight: -10 }
+      css/components/autocomplete-loading.css: { weight: -10 }
+      css/components/fieldgroup.css: { weight: -10 }
+      css/components/container-inline.css: { weight: -10 }
+      css/components/clearfix.css: { weight: -10 }
+      css/components/details.css: { weight: -10 }
+      css/components/hidden.css: { weight: -10 }
+      css/components/js.css: { weight: -10 }
+      css/components/nowrap.css: { weight: -10 }
+      css/components/position-container.css: { weight: -10 }
+      css/components/progress.css: { weight: -10 }
+      css/components/reset-appearance.css: { weight: -10 }
+      css/components/resize.css: { weight: -10 }
+      css/components/sticky-header.css: { weight: -10 }
+      css/components/tabledrag.css: { weight: -10 }
+      css/components/tree-child.css: { weight: -10 }
     theme:
       css/components/action-links.theme.css: { weight: -10 }
       css/components/breadcrumb.theme.css: { weight: -10 }
@@ -44,7 +45,6 @@ base:
       css/components/tablesort.theme.css: { weight: -10 }
       css/components/tabs.theme.css: { weight: -10 }
       css/components/textarea.theme.css: { weight: -10 }
-      css/components/tree-child.module.css: { weight: -10 }
 
 admin:
   version: VERSION
diff --git a/core/modules/toolbar/css/toolbar.module.css b/core/modules/toolbar/css/toolbar.css
similarity index 99%
rename from core/modules/toolbar/css/toolbar.module.css
rename to core/modules/toolbar/css/toolbar.css
index 69eb7c2..38b17a4 100644
--- a/core/modules/toolbar/css/toolbar.module.css
+++ b/core/modules/toolbar/css/toolbar.css
@@ -1,5 +1,5 @@
 /**
- * @file toolbar.module.css
+ * @file toolbar.css
  *
  *
  * Aggressive resets so we can achieve a consistent look in hostile CSS
diff --git a/core/modules/toolbar/toolbar.libraries.yml b/core/modules/toolbar/toolbar.libraries.yml
index dcef084..f71f856 100644
--- a/core/modules/toolbar/toolbar.libraries.yml
+++ b/core/modules/toolbar/toolbar.libraries.yml
@@ -13,7 +13,7 @@ toolbar:
     js/views/ToolbarVisualView.js: {}
   css:
     component:
-      css/toolbar.module.css: {}
+      css/toolbar.css: {}
     theme:
       css/toolbar.theme.css: {}
       css/toolbar.icons.theme.css: {}
diff --git a/core/modules/tour/css/tour.module.css b/core/modules/tour/css/tour.css
similarity index 100%
rename from core/modules/tour/css/tour.module.css
rename to core/modules/tour/css/tour.css
diff --git a/core/modules/tour/tour.libraries.yml b/core/modules/tour/tour.libraries.yml
index 9e57398..b0d5c28 100644
--- a/core/modules/tour/tour.libraries.yml
+++ b/core/modules/tour/tour.libraries.yml
@@ -14,4 +14,4 @@ tour-styling:
   version: VERSION
   css:
     component:
-      css/tour.module.css: { media: screen }
+      css/tour.css: { media: screen }
diff --git a/core/modules/user/css/user.module.css b/core/modules/user/css/user.css
similarity index 100%
rename from core/modules/user/css/user.module.css
rename to core/modules/user/css/user.css
diff --git a/core/modules/user/user.libraries.yml b/core/modules/user/user.libraries.yml
index e11cbfa..41651ff 100644
--- a/core/modules/user/user.libraries.yml
+++ b/core/modules/user/user.libraries.yml
@@ -4,7 +4,7 @@ drupal.user:
     user.js: {}
   css:
     component:
-      css/user.module.css: {}
+      css/user.css: {}
     theme:
       css/user.theme.css: {}
   dependencies:
diff --git a/core/modules/views/css/views.module.css b/core/modules/views/css/views.css
similarity index 100%
rename from core/modules/views/css/views.module.css
rename to core/modules/views/css/views.css
diff --git a/core/modules/views/views.libraries.yml b/core/modules/views/views.libraries.yml
index 03efb2c..dd6709a 100644
--- a/core/modules/views/views.libraries.yml
+++ b/core/modules/views/views.libraries.yml
@@ -2,7 +2,7 @@ views.module:
   version: VERSION
   css:
     component:
-      css/views.module.css: {}
+      css/views.css: {}
 
 views.ajax:
   version: VERSION