diff --git a/core/modules/system/templates/indentation.html.twig b/core/modules/system/templates/indentation.html.twig
index e5e7b32..8093d3f 100644
--- a/core/modules/system/templates/indentation.html.twig
+++ b/core/modules/system/templates/indentation.html.twig
@@ -17,4 +17,4 @@ See https://api.drupal.org/api/function/theme_indentation/8 for details.
 After copying this file to your theme's folder and customizing it, remove this
 HTML comment.
 -->
-{% for i in 1..size if size > 0 %}<div class="indentation">&nbsp;</div>{% endfor %}
+{% for i in 1..size if size > 0 %}<div>&nbsp;</div>{% endfor %}
diff --git a/core/modules/system/templates/install-page.html.twig b/core/modules/system/templates/install-page.html.twig
index 24d17fa..475042e 100644
--- a/core/modules/system/templates/install-page.html.twig
+++ b/core/modules/system/templates/install-page.html.twig
@@ -11,16 +11,16 @@
  * @ingroup themeable
  */
 #}
-  <div class="layout-container">
+  <div>
 
     <header role="banner">
       {% if site_name or site_slogan %}
-        <div class="name-and-slogan">
+        <div>
           {% if site_name %}
             <h1>{{ site_name }}</h1>
           {% endif %}
           {% if site_slogan %}
-            <div class="site-slogan">{{ site_slogan }}</div>
+            <div>{{ site_slogan }}</div>
           {% endif %}
         </div>{# /.name-and-slogan #}
       {% endif %}
@@ -35,13 +35,13 @@
     </main>
 
     {% if page.sidebar_first %}
-      <aside class="layout-sidebar-first" role="complementary">
+      <aside role="complementary">
         {{ page.sidebar_first }}
       </aside>{# /.layout-sidebar-first #}
     {% endif %}
 
     {% if page.sidebar_second %}
-      <aside class="layout-sidebar-second" role="complementary">
+      <aside role="complementary">
         {{ page.sidebar_second }}
       </aside>{# /.layout-sidebar-second #}
     {% endif %}
diff --git a/core/modules/system/templates/item-list.html.twig b/core/modules/system/templates/item-list.html.twig
index bd71e7f..fdb151e 100644
--- a/core/modules/system/templates/item-list.html.twig
+++ b/core/modules/system/templates/item-list.html.twig
@@ -19,7 +19,7 @@
  */
 #}
 {%- if items or empty -%}
-  <div class="item-list">
+  <div>
     {%- if title is not empty -%}
       <h3>{{ title }}</h3>
     {%- endif -%}
diff --git a/core/themes/classy/templates/image.html.twig b/core/themes/classy/templates/image.html.twig
new file mode 100644
index 0000000..2f29304
--- /dev/null
+++ b/core/themes/classy/templates/image.html.twig
@@ -0,0 +1,20 @@
+{#
+/**
+ * @file
+ * Default theme implementation of an image.
+ *
+ * Available variables:
+ * - attributes: HTML attributes for the img tag.
+ * - style_name: (optional) The name of the image style applied.
+ *
+ * @see template_preprocess_image()
+ *
+ * @ingroup themeable
+ */
+#}
+{%
+set classes = [
+  style_name ? 'image-style-' ~ style_name|clean_class,
+]
+%}
+<img{{ attributes.addClass(classes) }} />
diff --git a/core/themes/classy/templates/indentation.html.twig b/core/themes/classy/templates/indentation.html.twig
new file mode 100644
index 0000000..e5e7b32
--- /dev/null
+++ b/core/themes/classy/templates/indentation.html.twig
@@ -0,0 +1,20 @@
+{#
+/**
+ * @file
+ * Default theme implementation for a set of indentation divs.
+ *
+ * These <div> tags are used for drag and drop tables.
+ *
+ * Available variables:
+ * - size: Optional. The number of indentations to create.
+ *
+ * @ingroup themeable
+ */
+#}
+<!--
+THIS FILE IS NOT USED AND IS HERE AS A STARTING POINT FOR CUSTOMIZATION ONLY.
+See https://api.drupal.org/api/function/theme_indentation/8 for details.
+After copying this file to your theme's folder and customizing it, remove this
+HTML comment.
+-->
+{% for i in 1..size if size > 0 %}<div class="indentation">&nbsp;</div>{% endfor %}
diff --git a/core/themes/classy/templates/input.html.twig b/core/themes/classy/templates/input.html.twig
new file mode 100644
index 0000000..1409c25
--- /dev/null
+++ b/core/themes/classy/templates/input.html.twig
@@ -0,0 +1,15 @@
+{#
+/**
+ * @file
+ * Default theme implementation for an 'input' #type form element.
+ *
+ * Available variables:
+ * - attributes: A list of HTML attributes for the input element.
+ * - children: Optional additional rendered elements.
+ *
+ * @see template_preprocess_input()
+ *
+ * @ingroup themeable
+ */
+#}
+<input{{ attributes }} />{{ children }}
diff --git a/core/themes/classy/templates/install-page.html.twig b/core/themes/classy/templates/install-page.html.twig
new file mode 100644
index 0000000..24d17fa
--- /dev/null
+++ b/core/themes/classy/templates/install-page.html.twig
@@ -0,0 +1,55 @@
+{#
+/**
+ * @file
+ * Default theme implementation to display a Drupal installation page.
+ *
+ * All available variables are mirrored in page.html.twig.
+ * Some may be blank but they are provided for consistency.
+ *
+ * @see template_preprocess_install_page()
+ *
+ * @ingroup themeable
+ */
+#}
+  <div class="layout-container">
+
+    <header role="banner">
+      {% if site_name or site_slogan %}
+        <div class="name-and-slogan">
+          {% if site_name %}
+            <h1>{{ site_name }}</h1>
+          {% endif %}
+          {% if site_slogan %}
+            <div class="site-slogan">{{ site_slogan }}</div>
+          {% endif %}
+        </div>{# /.name-and-slogan #}
+      {% endif %}
+    </header>
+
+    <main role="main">
+      {% if title %}
+        <h1>{{ title }}</h1>
+      {% endif %}
+      {{ messages }}
+      {{ page.content }}
+    </main>
+
+    {% if page.sidebar_first %}
+      <aside class="layout-sidebar-first" role="complementary">
+        {{ page.sidebar_first }}
+      </aside>{# /.layout-sidebar-first #}
+    {% endif %}
+
+    {% if page.sidebar_second %}
+      <aside class="layout-sidebar-second" role="complementary">
+        {{ page.sidebar_second }}
+      </aside>{# /.layout-sidebar-second #}
+    {% endif %}
+
+    {% if page.footer %}
+      <footer role="contentinfo">
+        {{ page.footer }}
+      </footer>
+    {% endif %}
+
+  </div>{# /.layout-container #}
diff --git a/core/themes/classy/templates/item-list.html.twig b/core/themes/classy/templates/item-list.html.twig
new file mode 100644
index 0000000..bd71e7f
--- /dev/null
+++ b/core/themes/classy/templates/item-list.html.twig
@@ -0,0 +1,36 @@
+{#
+/**
+ * @file
+ * Default theme implementation for an item list.
+ *
+ * Available variables:
+ * - items: A list of items. Each item contains:
+ *   - attributes: HTML attributes to be applied to each list item.
+ *   - value: The content of the list element.
+ * - title: The title of the list.
+ * - list_type: The tag for list element ("ul" or "ol").
+ * - attributes: HTML attributes to be applied to the list.
+ * - empty: A message to display when there are no items. Allowed value is a
+ *   string or render array.
+ *
+ * @see template_preprocess_item_list()
+ *
+ * @ingroup themeable
+ */
+#}
+{%- if items or empty -%}
+  <div class="item-list">
+    {%- if title is not empty -%}
+      <h3>{{ title }}</h3>
+    {%- endif -%}
+    {%- if items -%}
+      <{{ list_type }}{{ attributes }}>
+        {%- for item in items -%}
+          <li{{ item.attributes }}>{{ item.value }}</li>
+        {%- endfor -%}
+      </{{ list_type }}>
+    {%- else -%}
+      {{- empty -}}
+    {%- endif -%}
+  </div>
+{%- endif %}