diff --git a/core/modules/block/templates/block-list.html.twig b/core/modules/block/templates/block-list.html.twig
index 474c654..f12f87d 100644
--- a/core/modules/block/templates/block-list.html.twig
+++ b/core/modules/block/templates/block-list.html.twig
@@ -13,11 +13,11 @@
  * @ingroup themeable
  */
 #}
-<div class="layout-block-list clearfix">
-  <div class="layout-region block-list-primary">
+<div>
+  <div>
     {{ form|without('place_blocks') }}
   </div>
-  <div class="layout-region block-list-secondary">
+  <div>
     {{ form.place_blocks }}
   </div>
 </div>
diff --git a/core/modules/block/templates/block.html.twig b/core/modules/block/templates/block.html.twig
index 2680121..3a32d75 100644
--- a/core/modules/block/templates/block.html.twig
+++ b/core/modules/block/templates/block.html.twig
@@ -33,13 +33,7 @@
  * @ingroup themeable
  */
 #}
-{%
-  set classes = [
-    'block',
-    'block-' ~ configuration.provider|clean_class,
-  ]
-%}
-<div{{ attributes.addClass(classes) }}>
+<div>
   {{ title_prefix }}
   {% if label %}
     <h2{{ title_attributes }}>{{ label }}</h2>
diff --git a/core/modules/block_content/templates/block-content-add-list.html.twig b/core/modules/block_content/templates/block-content-add-list.html.twig
index e5a5d97..0810461 100644
--- a/core/modules/block_content/templates/block-content-add-list.html.twig
+++ b/core/modules/block_content/templates/block-content-add-list.html.twig
@@ -15,7 +15,7 @@
  */
 #}
 {% spaceless %}
-  <dl class="node-type-list">
+  <dl>
     {% for type in types %}
       <dt>{{ type.link }}</dt>
       <dd>{{ type.description }}</dd>
diff --git a/core/themes/classy/templates/block/block-list.html.twig b/core/themes/classy/templates/block/block-list.html.twig
new file mode 100644
index 0000000..474c654
--- /dev/null
+++ b/core/themes/classy/templates/block/block-list.html.twig
@@ -0,0 +1,23 @@
+{#
+/**
+ * @file
+ * Two column template for the block add/edit form.
+ *
+ * This template will be used when a block edit form specifies 'block_edit_form'
+ * as its #theme callback.  Otherwise, by default, block add/edit forms will be
+ * themed by theme_form().
+ *
+ * Available variables:
+ * - form: The block add/edit form.
+ *
+ * @ingroup themeable
+ */
+#}
+<div class="layout-block-list clearfix">
+  <div class="layout-region block-list-primary">
+    {{ form|without('place_blocks') }}
+  </div>
+  <div class="layout-region block-list-secondary">
+    {{ form.place_blocks }}
+  </div>
+</div>
diff --git a/core/themes/classy/templates/block/block.html.twig b/core/themes/classy/templates/block/block.html.twig
new file mode 100644
index 0000000..2680121
--- /dev/null
+++ b/core/themes/classy/templates/block/block.html.twig
@@ -0,0 +1,51 @@
+{#
+/**
+ * @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.
+ *   - module: The module that provided this block plugin.
+ *   - cache: The cache settings.
+ *   - Block plugin specific settings will also be stored here.
+ * - block - The full block entity.
+ *   - label_hidden: The hidden block title value if the block was
+ *     configured to hide the title ('label' is empty in this case).
+ *   - module: The module that generated the block.
+ *   - delta: An ID for the block, unique within each module.
+ *   - region: The block region embedding the current block.
+ * - content: The content of this block.
+ * - attributes: HTML attributes for the containing element.
+ *   - id: A valid HTML ID and guaranteed unique.
+ * - title_attributes: HTML attributes for the title element.
+ * - content_attributes: HTML attributes for the content element.
+ * - 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
+ */
+#}
+{%
+  set classes = [
+    'block',
+    'block-' ~ configuration.provider|clean_class,
+  ]
+%}
+<div{{ attributes.addClass(classes) }}>
+  {{ title_prefix }}
+  {% if label %}
+    <h2{{ title_attributes }}>{{ label }}</h2>
+  {% endif %}
+  {{ title_suffix }}
+  {% block content %}
+    {{ content }}
+  {% endblock %}
+</div>
diff --git a/core/themes/classy/templates/block_content/block-content-add-list.html.twig b/core/themes/classy/templates/block_content/block-content-add-list.html.twig
new file mode 100644
index 0000000..e5a5d97
--- /dev/null
+++ b/core/themes/classy/templates/block_content/block-content-add-list.html.twig
@@ -0,0 +1,24 @@
+{#
+/**
+ * @file
+ * Default theme implementation to present a list of custom block types.
+ *
+ * Available variables:
+ * - types: A collection of all the available custom block types.
+ *   Each block type contains the following:
+ *   - link: A link to add a block of this type.
+ *   - description: A description of this custom block type.
+ *
+ * @see template_preprocess_block_content_add_list()
+ *
+ * @ingroup themeable
+ */
+#}
+{% spaceless %}
+  <dl class="node-type-list">
+    {% for type in types %}
+      <dt>{{ type.link }}</dt>
+      <dd>{{ type.description }}</dd>
+    {% endfor %}
+  </dl>
+{% endspaceless %}