Issue #2489474 by mortendk, LewisNyman, Manjit.Singh, davidhernandez: Move book.theme.css to Classy

core/modules/book/book.libraries.yml

@@ -7,8 +7,3 @@ drupal.book:
     - core/drupal
     - core/drupal.form
 
-navigation:
-  version: VERSION
-  css:
-    theme:
-      css/book.theme.css: {}

core/modules/book/book.module

@@ -243,11 +243,6 @@ function book_node_view(array &$build, EntityInterface $node, EntityViewDisplayI
       $build['book_navigation'] = array(
         '#markup' => drupal_render($book_navigation),
         '#weight' => 100,
-        '#attached' => [
-          'library' => [
-            'book/navigation',
-          ],
-        ],
         // The book navigation is a listing of Node entities, so associate its
         // list cache tag for correct invalidation.
         '#cache' => [

core/themes/classy/classy.libraries.yml

@@ -3,3 +3,9 @@ base:
   css:
     theme:
       css/layout.css: {}
+
+book-navigation:
+  version: VERSION
+  css:
+    theme:
+      css/navigation/book.theme.css: {}

core/themes/classy/templates/navigation/book-navigation.html.twig

@@ -28,6 +28,7 @@
  * @see template_preprocess_book_navigation()
  */
 #}
+{{ attach_library('classy/book-navigation') }}
 {% if tree or has_links %}
   <nav id="book-navigation-{{ book_id }}" class="book-navigation" role="navigation" aria-labelledby="book-label-{{ book_id }}">
     {{ tree }}