diff --git a/core/modules/block/block.admin.inc b/core/modules/block/block.admin.inc
index 72dc432..15cf9dc 100644
--- a/core/modules/block/block.admin.inc
+++ b/core/modules/block/block.admin.inc
@@ -139,7 +139,4 @@ function template_preprocess_block_admin_display_form(&$variables) {
     $variables['block_listing'][$region][$i]->operations = $block['operations'];
     $variables['block_listing'][$region][$i]->printed = FALSE;
   }
-
-  unset($children['blocks'], $children['block_regions']);
-  $variables['form_submit'] = drupal_render_children($children);
 }
diff --git a/core/modules/block/templates/block-admin-display-form.html.twig b/core/modules/block/templates/block-admin-display-form.html.twig
index 75661ec..e3ba40e 100644
--- a/core/modules/block/templates/block-admin-display-form.html.twig
+++ b/core/modules/block/templates/block-admin-display-form.html.twig
@@ -4,18 +4,18 @@
  * Default theme implementation to configure blocks.
  *
  * Available variables:
- * - block_regions: An array of regions. Keyed by name with the title as value.
- * - block_listing: An array of blocks keyed by region and then delta.
- * - form_submit: Form submit button.
+ * - block_regions: A collection of regions. Keyed by name with the title as value.
+ * - block_listing: A collection of blocks keyed by region and then delta.
+ * - form: The form elements.
  *
- * Each block_listing[region] contains an array of blocks for that region.
+ * Each block_listing[region] contains a collection of blocks for that region.
+ * - data: Each data in block_listing[region] contains.
+ *    - region_title: Region title for the listed block.
+ *    - block_title: Block title.
+ *    - region_select: Drop-down menu for assigning a region.
+ *    - weight_select: Drop-down menu for setting weights.
+ *    - operations: Block operations.
  *
- * Each data in block_listing[region] contains:
- * - data->region_title: Region title for the listed block.
- * - data->block_title: Block title.
- * - data->region_select: Drop-down menu for assigning a region.
- * - data->weight_select: Drop-down menu for setting weights.
- * - data->operations: Block operations.
  * @see template_preprocess()
  * @see template_preprocess_block_admin_display_form()
  *
@@ -53,4 +53,4 @@
   </tbody>
 </table>
 
-{{ form_submit }}
+{{ form }}