diff --git a/core/modules/toolbar/toolbar.libraries.yml b/core/modules/toolbar/toolbar.libraries.yml
index dcef084..334d275 100644
--- a/core/modules/toolbar/toolbar.libraries.yml
+++ b/core/modules/toolbar/toolbar.libraries.yml
@@ -14,9 +14,6 @@ toolbar:
   css:
     component:
       css/toolbar.module.css: {}
-    theme:
-      css/toolbar.theme.css: {}
-      css/toolbar.icons.theme.css: {}
   dependencies:
     - core/modernizr
     - core/jquery
diff --git a/core/modules/toolbar/toolbar.module b/core/modules/toolbar/toolbar.module
index ccf1f9c..d843b22 100644
--- a/core/modules/toolbar/toolbar.module
+++ b/core/modules/toolbar/toolbar.module
@@ -349,3 +349,44 @@ function _toolbar_get_subtrees_hash() {
   $hash = Crypt::hashBase64(serialize($subtrees));
   return [$hash, $cacheability];
 }
+
+/**
+ * Implements hook_library_info_alter().
+ *
+ * Includes additional stylesheets defined by the admin theme to allow it to
+ * customize the Administration toolbar appearance.
+ *
+ * An admin theme can specify CSS files to make the front-end administration
+ * experience of in-place editing match the administration experience in the
+ * back-end.
+ *
+ * The CSS files can be specified via the "toolbar_stylesheets" property in the
+ * .info.yml file:
+ * @code
+ * toolbar_stylesheets:
+ *   - css/toolbar.css
+ * @endcode
+ */
+function toolbar_library_info_alter(&$libraries, $extension) {
+  if ($extension === 'toolbar' && isset($libraries['toolbar'])) {
+    $theme = Drupal::config('system.theme')->get('admin');
+
+    // First let the base theme modify the library, then the actual theme.
+    $alter_library = function(&$library, $theme) use (&$alter_library) {
+      if (isset($theme) && $theme_path = drupal_get_path('theme', $theme)) {
+        $info = system_get_info('theme', $theme);
+        // Recurse to process base theme(s) first.
+        if (isset($info['base theme'])) {
+          $alter_library($library, $info['base theme']);
+        }
+        if (isset($info['toolbar_stylesheets'])) {
+          foreach ($info['toolbar_stylesheets'] as $path) {
+            $library['css']['theme']['/' . $theme_path . '/' . $path] = [];
+          }
+        }
+      }
+    };
+
+    $alter_library($libraries['toolbar'], $theme);
+  }
+}
diff --git a/core/modules/toolbar/css/toolbar.theme.css b/core/themes/seven/css/components/toolbar.css
similarity index 99%
rename from core/modules/toolbar/css/toolbar.theme.css
rename to core/themes/seven/css/components/toolbar.css
index a60e781..010ef49 100644
--- a/core/modules/toolbar/css/toolbar.theme.css
+++ b/core/themes/seven/css/components/toolbar.css
@@ -1,5 +1,5 @@
 /**
- * @file toolbar.theme.css
+ * @file toolbar.css
  */
 .toolbar {
   font-family: "Source Sans Pro", "Lucida Grande", Verdana, sans-serif;
diff --git a/core/modules/toolbar/css/toolbar.icons.theme.css b/core/themes/seven/css/components/toolbar.icons.css
similarity index 75%
rename from core/modules/toolbar/css/toolbar.icons.theme.css
rename to core/themes/seven/css/components/toolbar.icons.css
index 69f0df8..4d31885 100644
--- a/core/modules/toolbar/css/toolbar.icons.theme.css
+++ b/core/themes/seven/css/components/toolbar.icons.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(../../../../misc/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(../../../../misc/icons/ffffff/hamburger.svg);
 }
 .toolbar-bar .toolbar-icon-help:before {
-  background-image: url(../../../misc/icons/bebebe/questionmark-disc.svg);
+  background-image: url(../../../../misc/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(../../../../misc/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(../../../../misc/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(../../../../misc/icons/000000/file.svg);
 }
 .toolbar-icon-system-admin-structure:before {
-  background-image: url(../../../misc/icons/787878/orgchart.svg);
+  background-image: url(../../../../misc/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(../../../../misc/icons/000000/orgchart.svg);
 }
 .toolbar-icon-system-themes-page:before {
-  background-image: url(../../../misc/icons/787878/paintbrush.svg);
+  background-image: url(../../../../misc/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(../../../../misc/icons/000000/paintbrush.svg);
 }
 .toolbar-icon-entity-user-collection:before {
-  background-image: url(../../../misc/icons/787878/people.svg);
+  background-image: url(../../../../misc/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(../../../../misc/icons/000000/people.svg);
 }
 .toolbar-icon-system-modules-list:before {
-  background-image: url(../../../misc/icons/787878/puzzlepiece.svg);
+  background-image: url(../../../../misc/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(../../../../misc/icons/000000/puzzlepiece.svg);
 }
 .toolbar-icon-system-admin-config:before {
-  background-image: url(../../../misc/icons/787878/wrench.svg);
+  background-image: url(../../../../misc/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(../../../../misc/icons/000000/wrench.svg);
 }
 .toolbar-icon-system-admin-reports:before {
-  background-image: url(../../../misc/icons/787878/barchart.svg);
+  background-image: url(../../../../misc/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(../../../../misc/icons/000000/barchart.svg);
 }
 .toolbar-icon-help-main:before {
-  background-image: url(../../../misc/icons/787878/questionmark-disc.svg);
+  background-image: url(../../../../misc/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(../../../../misc/icons/000000/questionmark-disc.svg);
 }
 .toolbar .toolbar-bar .toolbar-icon:before {
   min-height: 3em;
@@ -238,24 +238,24 @@
   right: 1.6667em;
 }
 .toolbar .toolbar-icon.toolbar-handle:before {
-  background-image: url(../../../misc/icons/5181c6/chevron-disc-down.svg);
+  background-image: url(../../../../misc/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(../../../../misc/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(../../../../misc/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(../../../../misc/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(../../../../misc/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(../../../../misc/icons/bebebe/chevron-disc-right.svg);
 }
 /**
  * Orientation toggle.
@@ -282,24 +282,24 @@
  * 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(../../../../misc/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(../../../../misc/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(../../../../misc/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(../../../../misc/icons/787878/push-right.svg);
 }
 .toolbar .toolbar-toggle-orientation [value="horizontal"]:before {
-  background-image: url(../../../misc/icons/bebebe/push-up.svg);
+  background-image: url(../../../../misc/icons/bebebe/push-up.svg);
 }
 .toolbar .toolbar-toggle-orientation [value="horizontal"]:hover:before {
-  background-image: url(../../../misc/icons/787878/push-up.svg);
+  background-image: url(../../../../misc/icons/787878/push-up.svg);
 }
 
diff --git a/core/themes/seven/seven.info.yml b/core/themes/seven/seven.info.yml
index 1427896..9741ff5 100644
--- a/core/themes/seven/seven.info.yml
+++ b/core/themes/seven/seven.info.yml
@@ -13,6 +13,9 @@ stylesheets-remove:
   - '@classy/css/layout.css'
 quickedit_stylesheets:
   - css/components/quickedit.css
+toolbar_stylesheets:
+  - css/components/toolbar.css
+  - css/components/toolbar.icons.css
 regions:
   header: 'Header'
   pre_content: 'Pre-content'