diff --git a/core/modules/system/src/Tests/Form/ElementsDetailsTest.php b/core/modules/system/src/Tests/Form/ElementsDetailsTest.php
new file mode 100644
index 0000000..48c3bae
--- /dev/null
+++ b/core/modules/system/src/Tests/Form/ElementsDetailsTest.php
@@ -0,0 +1,54 @@
+<?php
+
+namespace Drupal\system\Tests\Form;
+
+use Drupal\simpletest\WebTestBase;
+
+/**
+ * Tests details element rendering and description placement.
+ *
+ * @group Form
+ */
+class ElementsDetailsTest extends WebTestBase {
+
+  /**
+   * Modules to enable.
+   *
+   * @var array
+   */
+  public static $modules = ['form_test'];
+
+  /**
+   * Tests different display options for details element descriptions.
+   */
+  public function testFieldsetDescriptions() {
+    $this->drupalGet('form-test/group-details');
+
+    // Check #description default placement.
+    $field_id = 'edit-meta';
+    $description_id = $field_id . '--description';
+    $elements = $this->xpath('//details[@id="' . $field_id . '" and @aria-describedby="' . $description_id . '"]//div/preceding-sibling::div');
+    $this->assertTrue(isset($elements[0]), 'Properly places by default the #description element before the form item within details group.');
+
+    // Check #description placement with #description_display='before'.
+    $field_id = 'edit-details-before';
+    $description_id = $field_id . '--description';
+    $elements = $this->xpath('//details[@id="' . $field_id . '" and @aria-describedby="' . $description_id . '"]//div[@id="edit-meta-before"]/preceding-sibling::div[@id="' . $description_id . '"]');
+    $this->assertTrue(isset($elements[0]), 'Properly places the #description element before the form item within details group.');
+
+    // Check #description placement with #description_display='after'.
+    $field_id = 'edit-details-after';
+    $description_id = $field_id . '--description';
+    $elements = $this->xpath('//details[@id="' . $field_id . '" and @aria-describedby="' . $description_id . '"]//div[@id="edit-meta-after"]/following-sibling::div[@id="' . $description_id . '"]');
+    $this->assertTrue(isset($elements[0]), 'Properly places the #description element after the form item within details group.');
+
+    // Check if the class is 'visually-hidden' on the form details description
+    // for the option with #description_display='invisible' and also check that
+    // the description is placed after the form element.
+    $field_id = 'edit-details-invisible';
+    $description_id = $field_id . '--description';
+    $elements = $this->xpath('//details[@id="' . $field_id . '" and @aria-describedby="' . $description_id . '"]//div[@id="edit-meta-invisible"]/following-sibling::div[contains(@class, "visually-hidden")]');
+    $this->assertTrue(isset($elements[0]), 'Properly renders the #description element visually-hidden within details group.');
+  }
+
+}
diff --git a/core/modules/system/src/Tests/Form/ElementsLabelsTest.php b/core/modules/system/src/Tests/Form/ElementsLabelsTest.php
index 2a57e5d..549e8e4 100644
--- a/core/modules/system/src/Tests/Form/ElementsLabelsTest.php
+++ b/core/modules/system/src/Tests/Form/ElementsLabelsTest.php
@@ -102,6 +102,13 @@ public function testFormLabels() {
   public function testFormDescriptions() {
     $this->drupalGet('form_test/form-descriptions');
 
+    // Check #description placement with no #description_display, so default is
+    // 'after' the form item.
+    $field_id = 'edit-form-textfield-test-description-default';
+    $description_id = $field_id . '--description';
+    $elements = $this->xpath('//input[@id="' . $field_id . '" and @aria-describedby="' . $description_id . '"]/following-sibling::div[@id="' . $description_id . '"]');
+    $this->assertTrue(isset($elements[0]), t('Properly places by default the #description element after the form item.'));
+
     // Check #description placement with #description_display='after'.
     $field_id = 'edit-form-textfield-test-description-after';
     $description_id = $field_id . '--description';
@@ -121,6 +128,37 @@ public function testFormDescriptions() {
     $description_id = $field_id . '--description';
     $elements = $this->xpath('//input[@id="' . $field_id . '" and @aria-describedby="' . $description_id . '"]/following-sibling::div[contains(@class, "visually-hidden")]');
     $this->assertTrue(isset($elements[0]), t('Properly renders the #description element visually-hidden.'));
+
+
+    $this->drupalGet('form-test/group-details');
+
+    // Check #description default placement in a 'details' element.
+    $field_id = 'edit-meta';
+    $description_id = $field_id . '--description';
+    $elements = $this->xpath('//details[@id="' . $field_id . '" and @aria-describedby="' . $description_id . '"]//div/preceding-sibling::div');
+    $this->assertTrue(isset($elements[0]), 'Properly places by default the #description element before the form item within details group.');
+
+    // Check #description placement with #description_display='before' in a
+    // 'details' element.
+    $field_id = 'edit-details-before';
+    $description_id = $field_id . '--description';
+    $elements = $this->xpath('//details[@id="' . $field_id . '" and @aria-describedby="' . $description_id . '"]//div[@id="edit-meta-before"]/preceding-sibling::div[@id="' . $description_id . '"]');
+    $this->assertTrue(isset($elements[0]), 'Properly places the #description element before the form item within details group.');
+
+    // Check #description placement with #description_display='after' in a
+    // 'details' element.
+    $field_id = 'edit-details-after';
+    $description_id = $field_id . '--description';
+    $elements = $this->xpath('//details[@id="' . $field_id . '" and @aria-describedby="' . $description_id . '"]//div[@id="edit-meta-after"]/following-sibling::div[@id="' . $description_id . '"]');
+    $this->assertTrue(isset($elements[0]), 'Properly places the #description element after the form item within details group.');
+
+    // Check if the class is 'visually-hidden' on the form details description
+    // for the option with #description_display='invisible' and also check that
+    // the description is placed after the form element.
+    $field_id = 'edit-details-invisible';
+    $description_id = $field_id . '--description';
+    $elements = $this->xpath('//details[@id="' . $field_id . '" and @aria-describedby="' . $description_id . '"]//div[@id="edit-meta-invisible"]/following-sibling::div[contains(@class, "visually-hidden")]');
+    $this->assertTrue(isset($elements[0]), 'Properly renders the #description element visually-hidden within details group.');
   }
 
   /**
diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestDescriptionForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestDescriptionForm.php
index 81120ad..bb8286b 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestDescriptionForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestDescriptionForm.php
@@ -23,6 +23,12 @@ public function getFormId() {
    * {@inheritdoc}
    */
   public function buildForm(array $form, FormStateInterface $form_state) {
+    $form['form_textfield_test_description_default'] = [
+      '#type' => 'textfield',
+      '#title' => 'Textfield test for description default after element',
+      '#description' => 'Textfield test for description default after element',
+    ];
+
     $form['form_textfield_test_description_before'] = [
       '#type' => 'textfield',
       '#title' => 'Textfield test for description before element',
diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestGroupDetailsForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestGroupDetailsForm.php
index 002b07d..304edf4 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestGroupDetailsForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestGroupDetailsForm.php
@@ -30,6 +30,7 @@ public function buildForm(array $form, FormStateInterface $form_state, $required
     $form['meta'] = [
       '#type' => 'details',
       '#title' => 'Group element',
+      '#description' => 'Details test for default description position.',
       '#open' => TRUE,
       '#group' => 'details',
     ];
@@ -37,6 +38,55 @@ public function buildForm(array $form, FormStateInterface $form_state, $required
       '#type' => 'textfield',
       '#title' => 'Nest in details element',
     ];
+
+    $form['details_before'] = [
+      '#type' => 'details',
+      '#title' => 'Details test for description before element',
+      '#description' => 'Details test for description before element.',
+      '#description_display' => 'before',
+    ];
+    $form['meta_before'] = [
+      '#type' => 'container',
+      '#title' => 'Group element',
+      '#group' => 'details_before',
+    ];
+    $form['meta_before']['element'] = [
+      '#type' => 'textfield',
+      '#title' => 'Nest in container element',
+    ];
+
+    $form['details_after'] = [
+      '#type' => 'details',
+      '#title' => 'Details test for description after element',
+      '#description' => 'Details test for description after element.',
+      '#description_display' => 'after',
+    ];
+    $form['meta_after'] = [
+      '#type' => 'container',
+      '#title' => 'Group element',
+      '#group' => 'details_after',
+    ];
+    $form['meta_after']['element'] = [
+      '#type' => 'textfield',
+      '#title' => 'Nest in container element',
+    ];
+
+    $form['details_invisible'] = [
+      '#type' => 'details',
+      '#title' => 'Details test for visually-hidden description',
+      '#description' => 'Details test for visually-hidden description.',
+      '#description_display' => 'invisible',
+    ];
+    $form['meta_invisible'] = [
+      '#type' => 'container',
+      '#title' => 'Group element',
+      '#group' => 'details_invisible',
+    ];
+    $form['meta_invisible']['element'] = [
+      '#type' => 'textfield',
+      '#title' => 'Nest in container element',
+    ];
+
     return $form;
   }