Update to Drupal 8.0.2. For more information, see https://www.drupal.org/drupal-8.0.2-release-notes

core/themes/stable/README.txt

@@ -0,0 +1,26 @@
+
+ABOUT STABLE
+------------
+
+Stable is the default base theme; it provides minimal markup and very few
+CSS classes. If you prefer more structured markup see the Classy base theme.
+
+Stable allows core markup and styling to evolve by functioning as a backwards
+compatibility layer for themes against changes to core markup and CSS. If you
+browse Stable's contents, you will find copies of all the Twig templates and
+CSS files provided by core.
+
+Stable will be used as the base theme if no base theme is set in a theme's
+.info.yml file. To opt out of Stable you can set the base theme to false in
+your theme's .info.yml file (see the warning below before doing this):
+  base theme: false
+
+Warning: Themes that opt out of using Stable as a base theme will need
+continuous maintenance as core changes, so only opt out if you are prepared to
+keep track of those changes and how they affect your theme.
+
+ABOUT DRUPAL THEMING
+--------------------
+
+For more information, see Drupal.org's theming guide.
+https://www.drupal.org/theme-guide/8

core/themes/stable/css/color/color.admin.css

@@ -74,6 +74,8 @@ button.color-palette__lock,
   left: -10px;
   direction: ltr;
   text-indent: -9999px;
+  border: 0;
+  outline: 0;
 }
 [dir="rtl"] button.color-palette__lock,
 [dir="rtl"] .color-palette__lock {

core/themes/stable/templates/form/container.html.twig

@@ -5,8 +5,10 @@
  *
  * Used for grouped form items. Can also be used as a theme wrapper for any
  * renderable element, to surround it with a <div> and HTML attributes.
- * See the @link forms_api_reference.html Form API reference @endlink for more
- * information on the #theme_wrappers render array property.
+ * See \Drupal\Core\Render\Element\RenderElement for more
+ * information on the #theme_wrappers render array property, and
+ * \Drupal\Core\Render\Element\container for usage of the container render
+ * element.
  *
  * Available variables:
  * - attributes: HTML attributes for the containing element.