diff --git a/core/modules/field/src/Tests/EntityReference/EntityReferenceFormatterTest.php b/core/modules/field/src/Tests/EntityReference/EntityReferenceFormatterTest.php
index d940188..0c4deb6 100644
--- a/core/modules/field/src/Tests/EntityReference/EntityReferenceFormatterTest.php
+++ b/core/modules/field/src/Tests/EntityReference/EntityReferenceFormatterTest.php
@@ -177,6 +177,10 @@ public function testEntityFormatter() {
     $formatter = 'entity_reference_entity_view';
     $build = $this->buildRenderArray([$this->referencedEntity, $this->unsavedReferencedEntity], $formatter);
 
+    // Enable the Classy theme.
+    \Drupal::service('theme_handler')->install(['classy']);
+    $this->config('system.theme')->set('default', 'classy')->save();
+
     // Test the first field item.
     $expected_rendered_name_field_1 = '<div class="field field-entity-test--name field-name-name field-type-string field-label-hidden">
     <div class="field-items">
diff --git a/core/modules/rdf/src/Tests/Field/NumberFieldRdfaTest.php b/core/modules/rdf/src/Tests/Field/NumberFieldRdfaTest.php
index f5974bb..49a831b 100644
--- a/core/modules/rdf/src/Tests/Field/NumberFieldRdfaTest.php
+++ b/core/modules/rdf/src/Tests/Field/NumberFieldRdfaTest.php
@@ -45,6 +45,11 @@ public function testIntegerFormatterWithSettings() {
       'prefix' => '#',
       'suffix' => ' llamas.',
     );
+
+    // Enable the Classy theme.
+    \Drupal::service('theme_handler')->install(['classy']);
+    $this->config('system.theme')->set('default', 'classy')->save();
+
     $this->createTestField($field_settings);
     $this->createTestEntity($testValue);
     $this->assertFormatterRdfa($formatter, 'http://schema.org/baseSalary', array('value' => $testValue));
@@ -87,6 +92,11 @@ public function testFloatFormatterWithSettings() {
       'prefix' => '$',
       'suffix' => ' more.',
     );
+
+    // Enable the Classy theme.
+    \Drupal::service('theme_handler')->install(['classy']);
+    $this->config('system.theme')->set('default', 'classy')->save();
+
     $this->createTestField($field_settings);
     $this->createTestEntity($testValue);
     $this->assertFormatterRdfa($formatter, 'http://schema.org/baseSalary', array('value' => $testValue));
@@ -129,6 +139,11 @@ public function testFloatFormatterWithScaleExercised() {
       ),
     );
     $testValue = 3.1234567;
+
+    // Enable the Classy theme.
+    \Drupal::service('theme_handler')->install(['classy']);
+    $this->config('system.theme')->set('default', 'classy')->save();
+
     $this->createTestField();
     $this->createTestEntity($testValue);
     $this->assertFormatterRdfa($formatter, 'http://schema.org/baseSalary', array('value' => $testValue));
@@ -171,6 +186,11 @@ public function testDecimalFormatterWithSettings() {
       'prefix' => '$',
       'suffix' => ' more.',
     );
+
+    // Enable the Classy theme.
+    \Drupal::service('theme_handler')->install(['classy']);
+    $this->config('system.theme')->set('default', 'classy')->save();
+
     $this->createTestField($field_settings);
     $this->createTestEntity($testValue);
     $this->assertFormatterRdfa($formatter, 'http://schema.org/baseSalary', array('value' => $testValue));
diff --git a/core/modules/system/templates/feed-icon.html.twig b/core/modules/system/templates/feed-icon.html.twig
index b3c10d1..a9e0f03 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 }}"{{ attributes }}>{{ 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 0745f84..fd41c13 100644
--- a/core/modules/system/templates/field.html.twig
+++ b/core/modules/system/templates/field.html.twig
@@ -38,30 +38,18 @@
  * @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{{ attributes }}>
   {% if not label_hidden %}
     <div{{ title_attributes.addClass(title_classes) }}>{{ 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..bb106d1 100644
--- a/core/modules/system/templates/fieldset.html.twig
+++ b/core/modules/system/templates/fieldset.html.twig
@@ -21,10 +21,9 @@
  * @ingroup themeable
  */
 #}
-<fieldset{{ attributes.addClass('form-item', 'form-wrapper') }}>
+<fieldset{{ attributes.addClass('form-wrapper') }}>
   {%
     set legend_span_classes = [
-      'fieldset-legend',
       required ? 'form-required',
     ]
   %}
diff --git a/core/modules/system/templates/form-element-label.html.twig b/core/modules/system/templates/form-element-label.html.twig
index 6ececd9..2bfd74a 100644
--- a/core/modules/system/templates/form-element-label.html.twig
+++ b/core/modules/system/templates/form-element-label.html.twig
@@ -16,7 +16,6 @@
 #}
 {%
   set classes = [
-    title_display == 'after' ? 'option',
     title_display == 'invisible' ? 'visually-hidden',
     required ? 'form-required',
   ]
diff --git a/core/modules/system/templates/form-element.html.twig b/core/modules/system/templates/form-element.html.twig
index a961801..f4be6cc 100644
--- a/core/modules/system/templates/form-element.html.twig
+++ b/core/modules/system/templates/form-element.html.twig
@@ -47,16 +47,11 @@
 #}
 {%
   set classes = [
-    'form-item',
-    'form-type-' ~ type|clean_class,
-    'form-item-' ~ name|clean_class,
-    title_display not in ['after', 'before'] ? 'form-no-label',
     disabled == 'disabled' ? 'form-disabled',
   ]
 %}
 {%
   set description_classes = [
-    'description',
     description_display == 'invisible' ? 'visually-hidden',
   ]
 %}
@@ -65,7 +60,7 @@
     {{ label }}
   {% endif %}
   {% if prefix is not empty %}
-    <span class="field-prefix">{{ prefix }}</span>
+    <span>{{ prefix }}</span>
   {% endif %}
   {% if description_display == 'before' and description.content %}
     <div{{ description.attributes }}>
@@ -74,7 +69,7 @@
   {% endif %}
   {{ children }}
   {% if suffix is not empty %}
-    <span class="field-suffix">{{ suffix }}</span>
+    <span>{{ suffix }}</span>
   {% endif %}
   {% if label_display == 'after' %}
     {{ label }}
diff --git a/core/themes/classy/templates/system/fieldset.html.twig b/core/themes/classy/templates/system/fieldset.html.twig
index ab6796c..5564850 100644
--- a/core/themes/classy/templates/system/fieldset.html.twig
+++ b/core/themes/classy/templates/system/fieldset.html.twig
@@ -21,10 +21,9 @@
  * @ingroup themeable
  */
 #}
-<fieldset{{ attributes.addClass('form-item', 'form-wrapper') }}>
+<fieldset{{ attributes.addClass('form-wrapper') }}>
   {%
     set legend_span_classes = [
-      'fieldset-legend',
       required ? 'form-required',
     ]
   %}
@@ -32,7 +31,7 @@
   <legend{{ legend.attributes }}>
     <span{{ legend_span.attributes.addClass(legend_span_classes) }}>{{ legend.title }}</span>
   </legend>
-  <div class="fieldset-wrapper">
+  <div>
     {% if prefix %}
       <span class="field-prefix">{{ prefix }}</span>
     {% endif %}