diff --git a/core/modules/media_library/css/media_library.theme.css b/core/modules/media_library/css/media_library.theme.css
index 92c52d69e1..197c3f0bd3 100644
--- a/core/modules/media_library/css/media_library.theme.css
+++ b/core/modules/media_library/css/media_library.theme.css
@@ -92,6 +92,12 @@
   margin: 0 0 1em;
 }
 
+/**
+ * Remove outline from added media container.
+ *
+ * The added media container receives focus after adding new media, but doesn't
+ * need the outline.
+ */
 .media-library-add-form__added-media {
   outline: none;
 }
diff --git a/core/modules/media_library/src/Form/AddFormBase.php b/core/modules/media_library/src/Form/AddFormBase.php
index d5ec0f16f1..7391879582 100644
--- a/core/modules/media_library/src/Form/AddFormBase.php
+++ b/core/modules/media_library/src/Form/AddFormBase.php
@@ -146,6 +146,8 @@ public function buildForm(array $form, FormStateInterface $form_state) {
           'class' => [
             'media-library-add-form__added-media',
           ],
+          // Add the tabindex '-1' to allow the focus to be shifted to the
+          // container.
           'tabindex' => -1,
           'aria-label' => $this->t('Added media items'),
         ],