diff --git a/core/modules/datetime/datetime.module b/core/modules/datetime/datetime.module
index 2b7d355..c8dd4d1 100644
--- a/core/modules/datetime/datetime.module
+++ b/core/modules/datetime/datetime.module
@@ -89,11 +89,6 @@ function datetime_theme() {
       'template' => 'datetime-wrapper',
       'render element' => 'element',
     ),
-    'fieldset' => array(
-      'template' => 'fieldset',
-      'render element' => 'element',
-      'path' => drupal_get_path('module', 'system') . '/templates/',
-    ),
   );
 }
 
diff --git a/core/modules/datetime/lib/Drupal/datetime/Plugin/Field/FieldWidget/DateTimeDefaultWidget.php b/core/modules/datetime/lib/Drupal/datetime/Plugin/Field/FieldWidget/DateTimeDefaultWidget.php
index ac39bfd..403a084 100644
--- a/core/modules/datetime/lib/Drupal/datetime/Plugin/Field/FieldWidget/DateTimeDefaultWidget.php
+++ b/core/modules/datetime/lib/Drupal/datetime/Plugin/Field/FieldWidget/DateTimeDefaultWidget.php
@@ -53,10 +53,8 @@ public function formElement(FieldItemListInterface $items, $delta, array $elemen
     // title because the actual title display is handled at a higher level by
     // the Field module.
 
-    $element['#theme_wrappers'][] = 'fieldset';
+    $element['#pre_render'][] = 'form_pre_render_conditional_form_element';
     $element['#attributes']['class'][] = 'container-inline';
-    $element['#attributes']['class'][] = 'fieldgroup';
-    $element['#attributes']['class'][] = 'form-composite';
     $element['#element_validate'][] = 'datetime_datetime_widget_validate';
 
     // Identify the type of date and time elements to use.
diff --git a/core/modules/system/css/system.module.css b/core/modules/system/css/system.module.css
index 24c1fea..d2961d6 100644
--- a/core/modules/system/css/system.module.css
+++ b/core/modules/system/css/system.module.css
@@ -270,8 +270,7 @@ tr .ajax-progress-throbber .throbber {
 .container-inline .details-wrapper {
   display: block;
 }
-/* Descriptions need to be rendered as block. */
-.container-inline .description {
+.container-inline > .description {
   display: block;
 }
 
diff --git a/core/modules/system/templates/fieldset.html.twig b/core/modules/system/templates/fieldset.html.twig
index d163c8c..9e4fe68 100644
--- a/core/modules/system/templates/fieldset.html.twig
+++ b/core/modules/system/templates/fieldset.html.twig
@@ -16,7 +16,6 @@
  * - children: The rendered child elements of the fieldset.
  * - prefix: The content to add before the fieldset children.
  * - suffix: The content to add after the fieldset children.
- * - content: The form element to be output.
  *
  * @see template_preprocess_fieldset()
  *
@@ -33,7 +32,6 @@
       <span class="field-prefix">{{ prefix }}</span>
     {% endif %}
     {{ children }}
-    {{ content }}
     {% if suffix %}
       <span class="field-suffix">{{ suffix }}</span>
     {% endif %}