DisplayModeLocalAction.php

<?php

namespace Drupal\field_ui;

use Drupal\Component\Serialization\Json;
use Drupal\Component\Utility\NestedArray;
use Drupal\Core\Menu\LocalActionDefault;
use Drupal\Core\Routing\RouteMatchInterface;

/**
 * Defines a local action plugin with modal dialog.
 */
class DisplayModeLocalAction extends LocalActionDefault {
  
  /**
   * {@inheritdoc}
   */
  public function getOptions(RouteMatchInterface $route_match) {
    $options = parent::getOptions($route_match);
    $options = NestedArray::mergeDeepArray([
      [
        'attributes' => [
          'class' => [
            'button',
            'use-ajax',
          ],
          'data-dialog-type' => 'modal',
          'data-dialog-options' => Json::encode([
            'width' => '880',
          ]),
        ],
      ],
      $options,
    ]);
    return $options;
  }

}