diff --git a/core/modules/outside_in/src/OffCanvasFormDialogTrait.php b/core/lib/Drupal/Core/Form/DialogFormTrait.php
similarity index 81%
rename from core/modules/outside_in/src/OffCanvasFormDialogTrait.php
rename to core/lib/Drupal/Core/Form/DialogFormTrait.php
index 62a76ba652..145a34ecfa 100644
--- a/core/modules/outside_in/src/OffCanvasFormDialogTrait.php
+++ b/core/lib/Drupal/Core/Form/DialogFormTrait.php
@@ -1,48 +1,29 @@
 <?php
 
-namespace Drupal\outside_in;
+namespace Drupal\Core\Form;
 
-use Drupal\Core\Ajax\AjaxResponse;
-use Drupal\Core\Ajax\CloseDialogCommand;
 use Drupal\Core\Ajax\RedirectCommand;
 use Drupal\Core\Ajax\ReplaceCommand;
 use Drupal\Core\EventSubscriber\MainContentViewSubscriber;
-use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Ajax\AjaxResponse;
+use Drupal\Core\Ajax\CloseDialogCommand;
 use Drupal\Core\Url;
 
 /**
- * Helper trait for forms that are used in the off-canvas dialog.
- *
- * Classes that use this trait should implement \Drupal\Core\Form\FormInterface.
+ * Provides utilities for forms that want to be rendered in dialogs.
  */
-trait OffCanvasFormDialogTrait {
+trait DialogFormTrait {
 
   /**
-   * Determines if the current request is for an AJAX modal dialog.
-   *
-   * @return bool
-   *   TRUE is the current request if for an AJAX modal dialog.
-   */
-  protected function isModalDialog() {
-    $wrapper_format = $this->getRequest()
-      ->get(MainContentViewSubscriber::WRAPPER_FORMAT);
-    return in_array($wrapper_format, [
-      'drupal_ajax',
-      'drupal_modal',
-      'drupal_dialog.off_canvas',
-    ]);
-  }
-
-  /**
-   * Adds modal dialog support to a form.
+   * Adds dialog support to a form.
    *
    * @param array $form
    *   An associative array containing the structure of the form.
    * @param \Drupal\Core\Form\FormStateInterface $form_state
    *   The current state of the form.
    */
-  protected function buildFormDialog(array &$form, FormStateInterface $form_state) {
-    if (!$this->isModalDialog()) {
+  protected function buildFormDialog(array &$form, FormStateInterface $form_state, $create_cancel = FALSE) {
+    if (!$this->isDialog()) {
       return;
     }
 
@@ -56,29 +37,64 @@ protected function buildFormDialog(array &$form, FormStateInterface $form_state)
       $ajax_callback_added = TRUE;
     }
 
-    if (!empty($form['actions']['cancel'])) {
-      // Replace 'Cancel' link button with a close dialog button.
+    if ($create_cancel) {
       $form['actions']['cancel'] = [
         '#type' => 'submit',
         '#value' => $this->t('Cancel'),
+        '#weight' => 100,
+      ];
+    }
+    if (!empty($form['actions']['cancel'])) {
+      // Replace 'Cancel' link button with a close dialog button.
+      $form['actions']['cancel'] = [
         '#submit' => ['::noSubmit'],
         '#limit_validation_errors' => [],
-        '#weight' => 100,
         '#ajax' => [
           'callback' => '::closeDialog',
           'event' => 'click',
         ],
-      ];
+      ] + $form['actions']['cancel'];
       $ajax_callback_added = TRUE;
     }
 
     if ($ajax_callback_added) {
       $form['#attached']['library'][] = 'core/drupal.dialog.ajax';
-      $form['#attributes']['id'] = 'off-canvas-form';
+      $form['#attributes']['id'] = 'dialog-form';
     }
   }
 
   /**
+   * Empty submit #ajax submit callback.
+   *
+   * This allows modal dialog to using ::submitCallback to validate and submit
+   * the form via one ajax required.
+   *
+   * @param array $form
+   *   An associative array containing the structure of the form.
+   * @param \Drupal\Core\Form\FormStateInterface $form_state
+   *   The current state of the form.
+   */
+  public function noSubmit(array &$form, FormStateInterface $form_state) {
+  }
+
+
+
+  /**
+   * Determines if the current request is for an AJAX dialog.
+   *
+   * @return bool
+   *   TRUE is the current request if for an AJAX dialog.
+   */
+  protected function isDialog() {
+    return in_array($this->getRequestWrapperFormat(), [
+      'drupal_ajax',
+      'drupal_dialog',
+      'drupal_modal',
+      'drupal_dialog.off_canvas',
+    ]);
+  }
+
+  /**
    * Submit form dialog #ajax callback.
    *
    * @param array $form
@@ -97,7 +113,7 @@ public function submitFormDialog(array &$form, FormStateInterface $form_state) {
         '#type' => 'status_messages',
         '#weight' => -1000,
       ];
-      $command = new ReplaceCommand('#off-canvas-form', $form);
+      $command = new ReplaceCommand('#dialog-form', $form);
     }
     else {
       if ($redirect_url = $this->getRedirectUrl()) {
@@ -122,21 +138,16 @@ public function submitFormDialog(array &$form, FormStateInterface $form_state) {
    *   An AJAX response that display validation error messages.
    */
   public function closeDialog(array &$form, FormStateInterface $form_state) {
-    return (new AjaxResponse())->addCommand(new CloseDialogCommand('#drupal-off-canvas'));
+    return (new AjaxResponse())->addCommand(new CloseDialogCommand($this->getDialogSelector()));
   }
 
   /**
-   * Empty submit #ajax submit callback.
-   *
-   * This allows modal dialog to using ::submitCallback to validate and submit
-   * the form via one ajax required.
-   *
-   * @param array $form
-   *   An associative array containing the structure of the form.
-   * @param \Drupal\Core\Form\FormStateInterface $form_state
-   *   The current state of the form.
+   * @return mixed
    */
-  public function noSubmit(array &$form, FormStateInterface $form_state) {
+  protected function getRequestWrapperFormat() {
+    $wrapper_format = $this->getRequest()
+      ->get(MainContentViewSubscriber::WRAPPER_FORMAT);
+    return $wrapper_format;
   }
 
   /**
@@ -180,12 +191,15 @@ protected function getRedirectDestinationPath() {
   }
 
   /**
-   * Implements \Drupal\Core\Form\FormInterface::buildForm().
+   * @return string
    */
-  public function buildForm(array $form, FormStateInterface $form_state) {
-    $form = parent::buildForm($form, $form_state);
-    $this->buildFormDialog($form, $form_state);
-    return $form;
+  protected function getDialogSelector() {
+    if ($this->getRequestWrapperFormat() === 'drupal_dialog.off_canvas') {
+      return '#drupal-off-canvas';
+    }
+    else {
+      return '#drupal-modal';
+    }
   }
 
 }
diff --git a/core/modules/outside_in/src/Block/BlockEntityOffCanvasForm.php b/core/modules/outside_in/src/Block/BlockEntityOffCanvasForm.php
index 709f922e6d..58d287fed8 100644
--- a/core/modules/outside_in/src/Block/BlockEntityOffCanvasForm.php
+++ b/core/modules/outside_in/src/Block/BlockEntityOffCanvasForm.php
@@ -5,9 +5,9 @@
 use Drupal\block\BlockForm;
 use Drupal\block\BlockInterface;
 use Drupal\Core\Block\BlockPluginInterface;
+use Drupal\Core\Form\DialogFormTrait;
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\Plugin\PluginWithFormsInterface;
-use Drupal\outside_in\OffCanvasFormDialogTrait;
 
 /**
  * Provides form for block instance forms when used in the off-canvas dialog.
@@ -17,7 +17,7 @@
  */
 class BlockEntityOffCanvasForm extends BlockForm {
 
-  use OffCanvasFormDialogTrait;
+  use DialogFormTrait;
 
   /**
    * Provides a title callback to get the block's admin label.
@@ -123,4 +123,13 @@ public function submitForm(array &$form, FormStateInterface $form_state) {
     $form_state->disableRedirect();
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function buildForm(array $form, FormStateInterface $form_state) {
+    $form = parent::buildForm($form, $form_state);
+    $this->buildFormDialog($form, $form_state);
+    return $form;
+  }
+
 }
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 8a12d192d9..64b14e8e6c 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
@@ -2,16 +2,16 @@
 
 namespace Drupal\off_canvas_test\Form;
 
+use Drupal\Core\Form\DialogFormTrait;
 use Drupal\Core\Form\FormBase;
 use Drupal\Core\Form\FormStateInterface;
-use Drupal\outside_in\OffCanvasFormDialogTrait;
 
 /**
  * Just a test form.
  */
 class TestForm extends FormBase {
 
-  use OffCanvasFormDialogTrait;
+  use DialogFormTrait;
 
   /**
    * {@inheritdoc}