diff --git a/core/modules/outside_in/css/outside_in.module.css b/core/modules/outside_in/css/outside_in.module.css
index a0bb4a32aa..9d90bf227d 100644
--- a/core/modules/outside_in/css/outside_in.module.css
+++ b/core/modules/outside_in/css/outside_in.module.css
@@ -22,11 +22,6 @@
   pointer-events: inherit;
 }
 
-.ui-dialog-off-canvas .messages__wrapper:empty {
-  padding: 0;
-  margin: 0;
-}
-
 /*
  * Force the tray to be 100% width at the same breakpoint the dialog system uses
  * to expand dialog widths.
diff --git a/core/modules/outside_in/src/Block/BlockEntityOffCanvasForm.php b/core/modules/outside_in/src/Block/BlockEntityOffCanvasForm.php
index fb290225c2..709f922e6d 100644
--- a/core/modules/outside_in/src/Block/BlockEntityOffCanvasForm.php
+++ b/core/modules/outside_in/src/Block/BlockEntityOffCanvasForm.php
@@ -39,7 +39,6 @@ public function title(BlockInterface $block) {
    */
   public function form(array $form, FormStateInterface $form_state) {
     $form = parent::form($form, $form_state);
-    $form['#attributes']['data-off-canvas-form'] = TRUE;
 
     // Create link to full block form.
     $query = [];
@@ -118,8 +117,9 @@ protected function getPluginForm(BlockPluginInterface $block) {
    */
   public function submitForm(array &$form, FormStateInterface $form_state) {
     parent::submitForm($form, $form_state);
-    // \Drupal\block\BlockForm::submitForm() always redirects to block listing.
-    // This would doesn't work with Ajax submit.
+    // \Drupal\block\BlockForm::submitForm() always redirects to block listing
+    // via \Drupal\Core\Form\FormStateInterface::setRedirect(). This method
+    // does not work with Ajax submit.
     $form_state->disableRedirect();
   }
 
diff --git a/core/modules/outside_in/src/OffCanvasFormDialogTrait.php b/core/modules/outside_in/src/OffCanvasFormDialogTrait.php
index 391d7801c8..62a76ba652 100644
--- a/core/modules/outside_in/src/OffCanvasFormDialogTrait.php
+++ b/core/modules/outside_in/src/OffCanvasFormDialogTrait.php
@@ -140,7 +140,7 @@ public function noSubmit(array &$form, FormStateInterface $form_state) {
   }
 
   /**
-   * Get the form's redirect URL.
+   * Gets the form's redirect URL.
    *
    * Isolate a form's redirect URL/destination so that it can be used by
    * ::submitFormDialog or ::submitForm.
@@ -153,7 +153,7 @@ protected function getRedirectUrl() {
   }
 
   /**
-   * Get the URL from the destination service.
+   * Gets the URL from the destination service.
    *
    * @return \Drupal\Core\Url|null
    *   The destination URL or NULL no destination available.
@@ -165,7 +165,7 @@ protected function getDestinationUrl() {
   }
 
   /**
-   * Get the redirect destination path if specified in request.
+   * Gets the redirect destination path if specified in request.
    *
    * \Drupal\Core\Routing\RedirectDestination::get() cannot be used directly
    * because it will use <current> if 'destination' is not in the query string.
diff --git a/core/modules/outside_in/src/Tests/Ajax/OffCanvasDialogTest.php b/core/modules/outside_in/src/Tests/Ajax/OffCanvasDialogTest.php
index bf940ce9d5..edf055b577 100644
--- a/core/modules/outside_in/src/Tests/Ajax/OffCanvasDialogTest.php
+++ b/core/modules/outside_in/src/Tests/Ajax/OffCanvasDialogTest.php
@@ -36,7 +36,7 @@ public function testDialog() {
       'command' => 'openDialog',
       'selector' => '#drupal-off-canvas',
       'settings' => NULL,
-      'data' => $dialog_contents . "<div class=\"messages__wrapper\"></div>\n",
+      'data' => $dialog_contents,
       'dialogOptions' =>
         [
           'title' => 'AJAX Dialog & contents',
diff --git a/core/modules/outside_in/tests/modules/off_canvas_test/src/Form/TestForm.php b/core/modules/outside_in/tests/modules/off_canvas_test/src/Form/TestForm.php
index e561e9f595..8a12d192d9 100644
--- a/core/modules/outside_in/tests/modules/off_canvas_test/src/Form/TestForm.php
+++ b/core/modules/outside_in/tests/modules/off_canvas_test/src/Form/TestForm.php
@@ -24,7 +24,6 @@ public function getFormId() {
    * {@inheritdoc}
    */
   public function buildForm(array $form, FormStateInterface $form_state) {
-    $form['#attributes']['data-off-canvas-form'] = TRUE;
     $form['force_error'] = [
       '#type' => 'checkbox',
       '#title' => $this->t('Force error?'),