diff --git a/core/modules/system/templates/details.html.twig b/core/modules/system/templates/details.html.twig
index 17ea820..42dd4c2 100644
--- a/core/modules/system/templates/details.html.twig
+++ b/core/modules/system/templates/details.html.twig
@@ -19,9 +19,9 @@
   {%- if title -%}
     <summary{{ summary_attributes }}>{{ title }}</summary>
   {%- endif -%}
-  <div class="details-wrapper">
+  <div>
     {%- if description -%}
-      <div class="details-description">{{ description }}</div>
+      <div>{{ description }}</div>
     {%- endif -%}
     {%- if children -%}
       {{ children }}
diff --git a/core/modules/system/templates/dropbutton-wrapper.html.twig b/core/modules/system/templates/dropbutton-wrapper.html.twig
index ca0ff7e..599c6d8 100644
--- a/core/modules/system/templates/dropbutton-wrapper.html.twig
+++ b/core/modules/system/templates/dropbutton-wrapper.html.twig
@@ -14,8 +14,8 @@
 #}
 {% if children %}
   {% spaceless %}
-    <div class="dropbutton-wrapper">
-      <div class="dropbutton-widget">
+    <div>
+      <div>
         {{ children }}
       </div>
     </div>
diff --git a/core/modules/system/templates/feed-icon.html.twig b/core/modules/system/templates/feed-icon.html.twig
index b3c10d1..a08628c 100644
--- a/core/modules/system/templates/feed-icon.html.twig
+++ b/core/modules/system/templates/feed-icon.html.twig
@@ -15,4 +15,4 @@
  * @ingroup themeable
  */
 #}
-<a href="{{ url }}"{{ attributes.addClass('feed-icon') }}>{{ icon }}</a>
+<a href="{{ url }}">{{ icon }}</a>
diff --git a/core/modules/system/templates/field-multiple-value-form.html.twig b/core/modules/system/templates/field-multiple-value-form.html.twig
index f18a853..e9370e9 100644
--- a/core/modules/system/templates/field-multiple-value-form.html.twig
+++ b/core/modules/system/templates/field-multiple-value-form.html.twig
@@ -20,13 +20,13 @@
  */
 #}
 {% if multiple %}
-  <div class="form-item">
+  <div>
     {{ table }}
     {% if description %}
-      <div class="description">{{ description }}</div>
+      <div>{{ description }}</div>
     {% endif %}
     {% if button %}
-      <div class="clearfix">{{ button }}</div>
+      <div>{{ button }}</div>
     {% endif %}
   </div>
 {% else %}
diff --git a/core/modules/system/templates/field.html.twig b/core/modules/system/templates/field.html.twig
index 5fcfd4f..c4cee6c 100644
--- a/core/modules/system/templates/field.html.twig
+++ b/core/modules/system/templates/field.html.twig
@@ -34,30 +34,14 @@
  * @ingroup themeable
  */
 #}
-{% set field_name_class = field_name|clean_class %}
-{%
-  set classes = [
-    'field',
-    'field-' ~ entity_type|clean_class ~ '--' ~ field_name_class,
-    'field-name-' ~ field_name_class,
-    'field-type-' ~ field_type|clean_class,
-    'field-label-' ~ label_display,
-    label_display == 'inline' ? 'clearfix',
-  ]
-%}
-{%
-  set title_classes = [
-    'field-label',
-    label_display == 'visually_hidden' ? 'visually-hidden',
-  ]
-%}
-<div{{ attributes.addClass(classes) }}>
+
+<div>
   {% if not label_hidden %}
-    <div{{ title_attributes.addClass(title_classes) }}>{{ label }}</div>
+    <div{{ title_attributes }}>{{ label }}</div>
   {% endif %}
-  <div{{ content_attributes.addClass('field-items') }}>
+  <div{{ content_attributes }}>
     {% for item in items %}
-      <div{{ item.attributes.addClass('field-item') }}>{{ item.content }}</div>
+      <div{{ item.attributes }}>{{ item.content }}</div>
     {% endfor %}
   </div>
 </div>
diff --git a/core/modules/system/templates/fieldset.html.twig b/core/modules/system/templates/fieldset.html.twig
index ab6796c..1765135 100644
--- a/core/modules/system/templates/fieldset.html.twig
+++ b/core/modules/system/templates/fieldset.html.twig
@@ -21,27 +21,21 @@
  * @ingroup themeable
  */
 #}
-<fieldset{{ attributes.addClass('form-item', 'form-wrapper') }}>
-  {%
-    set legend_span_classes = [
-      'fieldset-legend',
-      required ? 'form-required',
-    ]
-  %}
+<fieldset>
   {#  Always wrap fieldset legends in a SPAN for CSS positioning. #}
   <legend{{ legend.attributes }}>
-    <span{{ legend_span.attributes.addClass(legend_span_classes) }}>{{ legend.title }}</span>
+    <span>{{ legend.title }}</span>
   </legend>
-  <div class="fieldset-wrapper">
+  <div>
     {% if prefix %}
-      <span class="field-prefix">{{ prefix }}</span>
+      <span>{{ prefix }}</span>
     {% endif %}
     {{ children }}
     {% if suffix %}
-      <span class="field-suffix">{{ suffix }}</span>
+      <span>{{ suffix }}</span>
     {% endif %}
     {% if description.content %}
-      <div{{ description.attributes.addClass('description') }}>{{ description.content }}</div>
+      <div{{ description.attributes }}>{{ description.content }}</div>
     {% endif %}
   </div>
 </fieldset>
diff --git a/core/modules/system/templates/form-element-label.html.twig b/core/modules/system/templates/form-element-label.html.twig
index 6ececd9..852e429 100644
--- a/core/modules/system/templates/form-element-label.html.twig
+++ b/core/modules/system/templates/form-element-label.html.twig
@@ -14,13 +14,7 @@
  * @ingroup themeable
  */
 #}
-{%
-  set classes = [
-    title_display == 'after' ? 'option',
-    title_display == 'invisible' ? 'visually-hidden',
-    required ? 'form-required',
-  ]
-%}
+
 {% if title is not empty or required -%}
-  <label{{ attributes.addClass(classes) }}>{{ title }}</label>
+  <label{{ attributes }}>{{ title }}</label>
 {%- endif %}
diff --git a/core/modules/system/templates/details.html.twig b/core/themes/classy/templates/details.html.twig
similarity index 100%
copy from core/modules/system/templates/details.html.twig
copy to core/themes/classy/templates/details.html.twig
diff --git a/core/modules/system/templates/dropbutton-wrapper.html.twig b/core/themes/classy/templates/dropbutton-wrapper.html.twig
similarity index 100%
copy from core/modules/system/templates/dropbutton-wrapper.html.twig
copy to core/themes/classy/templates/dropbutton-wrapper.html.twig
diff --git a/core/modules/system/templates/feed-icon.html.twig b/core/themes/classy/templates/feed-icon.html.twig
similarity index 100%
copy from core/modules/system/templates/feed-icon.html.twig
copy to core/themes/classy/templates/feed-icon.html.twig
diff --git a/core/modules/system/templates/field-multiple-value-form.html.twig b/core/themes/classy/templates/field-multiple-value-form.html.twig
similarity index 100%
copy from core/modules/system/templates/field-multiple-value-form.html.twig
copy to core/themes/classy/templates/field-multiple-value-form.html.twig
diff --git a/core/modules/system/templates/field.html.twig b/core/themes/classy/templates/field.html.twig
similarity index 100%
copy from core/modules/system/templates/field.html.twig
copy to core/themes/classy/templates/field.html.twig
diff --git a/core/modules/system/templates/fieldset.html.twig b/core/themes/classy/templates/fieldset.html.twig
similarity index 100%
copy from core/modules/system/templates/fieldset.html.twig
copy to core/themes/classy/templates/fieldset.html.twig
diff --git a/core/modules/system/templates/form-element-label.html.twig b/core/themes/classy/templates/form-element-label.html.twig
similarity index 100%
copy from core/modules/system/templates/form-element-label.html.twig
copy to core/themes/classy/templates/form-element-label.html.twig