Resolve #3504785 "1.0.x"

Closes #3504785

templates/overrides/system/block--system-menu-block.html.twig

+{#
+/**
+ * @file
+ * Default theme implementation to display a block.
+ *
+ * Available variables:
+ * - plugin_id: The ID of the block implementation.
+ * - label: The configured label of the block if visible.
+ * - configuration: A list of the block's configuration values.
+ *   - label: The configured label for the block.
+ *   - label_display: The display settings for the label.
+ *   - provider: The module or other provider that provided this block plugin.
+ *   - Block plugin specific settings will also be stored here.
+ * - content: The content of this block.
+ * - attributes: array of HTML attributes populated by modules, intended to
+ *   be added to the main container tag of this template.
+ *   - id: A valid HTML ID and guaranteed unique.
+ * - title_attributes: Same as attributes, except applied to the main title
+ *   tag that appears in the template.
+ * - title_prefix: Additional output populated by modules, intended to be
+ *   displayed in front of the main title tag that appears in the template.
+ * - title_suffix: Additional output populated by modules, intended to be
+ *   displayed after the main title tag that appears in the template.
+ *
+ * @see template_preprocess_block()
+ *
+ * @ingroup themeable
+ */
+#}
+{% if attributes.storage() %}
+<div{{ attributes }}>
+{% endif %}
+
+{{ title_prefix }}
+{% if label %}
+  <h2{{ title_attributes }}>{{ label }}</h2>
+{% endif %}
+{{ title_suffix }}
+{% block content %}
+  {{ content }}
+{% endblock %}
+
+{% if attributes.storage() %}
+</div>
+{% endif %}