diff -u b/core/modules/aggregator/lib/Drupal/aggregator/Plugin/Block/AggregatorCategoryBlock.php b/core/modules/aggregator/lib/Drupal/aggregator/Plugin/Block/AggregatorCategoryBlock.php
--- b/core/modules/aggregator/lib/Drupal/aggregator/Plugin/Block/AggregatorCategoryBlock.php
+++ b/core/modules/aggregator/lib/Drupal/aggregator/Plugin/Block/AggregatorCategoryBlock.php
@@ -77,7 +77,7 @@
         ),
       );
       $container = array(
-        '#theme' => 'container',
+        '#theme_wrappers' => array('container'),
         'more_link' => $more_link,
         '#attributes' => array(
           'class' => array('more-link'),
diff -u b/core/modules/aggregator/lib/Drupal/aggregator/Plugin/Block/AggregatorFeedBlock.php b/core/modules/aggregator/lib/Drupal/aggregator/Plugin/Block/AggregatorFeedBlock.php
--- b/core/modules/aggregator/lib/Drupal/aggregator/Plugin/Block/AggregatorFeedBlock.php
+++ b/core/modules/aggregator/lib/Drupal/aggregator/Plugin/Block/AggregatorFeedBlock.php
@@ -78,7 +78,7 @@
         ),
       );
       $container = array(
-        '#theme' => 'container',
+        '#theme_wrappers' => array('container'),
         'more_link' => $more_link,
         '#attributes' => array(
           'class' => array('more-link'),
diff -u b/core/modules/forum/forum.module b/core/modules/forum/forum.module
--- b/core/modules/forum/forum.module
+++ b/core/modules/forum/forum.module
@@ -50,7 +50,7 @@
         '#title' => t('More help'),
       );
       $container = array(
-        '#theme' => 'container',
+        '#theme_wrappers' => array('container'),
         'more_help_link' => $more_help_link,
         '#attributes' => array(
           'class' => array('more-help-link'),
@@ -657,7 +657,7 @@
       ),
     );
     $elements['forum_more'] = array(
-      '#theme' => 'container',
+      '#theme_wrappers' => array('container'),
       'more_link' => $more_link,
       '#attributes' => array(
         'class' => array('more-link'),
diff -u b/core/modules/node/node.module b/core/modules/node/node.module
--- b/core/modules/node/node.module
+++ b/core/modules/node/node.module
@@ -1552,7 +1552,7 @@
         ),
       );
       $container = array(
-        '#theme' => 'container',
+        '#theme_wrappers' => array('container'),
         'more_link' => $more_link,
         '#attributes' => array(
           'class' => array('more-link'),
diff -u b/core/modules/system/tests/modules/theme_test/lib/Drupal/theme_test/EventSubscriber/ThemeTestSubscriber.php b/core/modules/system/tests/modules/theme_test/lib/Drupal/theme_test/EventSubscriber/ThemeTestSubscriber.php
--- b/core/modules/system/tests/modules/theme_test/lib/Drupal/theme_test/EventSubscriber/ThemeTestSubscriber.php
+++ b/core/modules/system/tests/modules/theme_test/lib/Drupal/theme_test/EventSubscriber/ThemeTestSubscriber.php
@@ -39,11 +39,11 @@
         '#href' => 'user',
         '#title' => t('More'),
         '#attributes' => array(
-          '#title' => t('Themed output generated in a KernelEvents::REQUEST listener'),
+          '#title' => 'Themed output generated in a KernelEvents::REQUEST listener',
         ),
       );
       $container = array(
-        '#theme' => 'container',
+        '#theme_wrappers' => array('container'),
         'more_link' => $more_link,
         '#attributes' => array(
           'class' => array('more-link'),