diff --git a/core/includes/form.inc b/core/includes/form.inc
index efb59f7..b7fe0c2 100644
--- a/core/includes/form.inc
+++ b/core/includes/form.inc
@@ -1062,6 +1062,7 @@ function template_preprocess_fieldset(&$variables) {
   _form_set_attributes($element, array('form-wrapper'));
   $variables['attributes'] = $element['#attributes'];
   $variables['attributes']['class'][] = 'form-item';
+  $variables['attributes']['class'][] = 'field-group';
 
   // If the element is required, a required marker is appended to the label.
   $variables['required'] = '';
diff --git a/core/modules/datetime/datetime.module b/core/modules/datetime/datetime.module
index c8dd4d1..2b7d355 100644
--- a/core/modules/datetime/datetime.module
+++ b/core/modules/datetime/datetime.module
@@ -89,6 +89,11 @@ 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 ca60f4a..3979273 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
@@ -53,7 +53,7 @@ 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'][] = 'datetime_wrapper';
+    $element['#theme_wrappers'][] = 'fieldset';
     $element['#attributes']['class'][] = 'container-inline';
     $element['#element_validate'][] = 'datetime_datetime_widget_validate';
 
diff --git a/core/modules/datetime/lib/Drupal/datetime/Tests/DateTimeFieldTest.php b/core/modules/datetime/lib/Drupal/datetime/Tests/DateTimeFieldTest.php
index 0302c72..4143f03 100644
--- a/core/modules/datetime/lib/Drupal/datetime/Tests/DateTimeFieldTest.php
+++ b/core/modules/datetime/lib/Drupal/datetime/Tests/DateTimeFieldTest.php
@@ -98,7 +98,7 @@ function testDateField() {
     // Display creation form.
     $this->drupalGet('entity_test/add');
     $this->assertFieldByName("{$field_name}[0][value][date]", '', 'Date element found.');
-    $this->assertFieldByXPath('//*[@id="edit-' . $field_name . '-wrapper"]/h4/span', '*', 'Required markup found');
+    $this->assertFieldByXPath('//*[@id="edit-' . $field_name .'-wrapper"]/fieldset/legend/span', '*', 'Required markup found');
     $this->assertNoFieldByName("{$field_name}[0][value][time]", '', 'Time element not found.');
 
     // Submit a valid date and ensure it is accepted.
diff --git a/core/modules/system/css/system.module.css b/core/modules/system/css/system.module.css
index a74934f..24c1fea 100644
--- a/core/modules/system/css/system.module.css
+++ b/core/modules/system/css/system.module.css
@@ -270,6 +270,10 @@ tr .ajax-progress-throbber .throbber {
 .container-inline .details-wrapper {
   display: block;
 }
+/* Descriptions need to be rendered as block. */
+.container-inline .description {
+  display: block;
+}
 
 /**
  * Prevent text wrapping.
diff --git a/core/modules/system/templates/fieldset.html.twig b/core/modules/system/templates/fieldset.html.twig
index 9e4fe68..d163c8c 100644
--- a/core/modules/system/templates/fieldset.html.twig
+++ b/core/modules/system/templates/fieldset.html.twig
@@ -16,6 +16,7 @@
  * - 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()
  *
@@ -32,6 +33,7 @@
       <span class="field-prefix">{{ prefix }}</span>
     {% endif %}
     {{ children }}
+    {{ content }}
     {% if suffix %}
       <span class="field-suffix">{{ suffix }}</span>
     {% endif %}