uswds-8.x-2.1-rc1/form/node.form.inc

<?php

/**
 * @file
 * Alterations for this form.
 */

use Drupal\Core\Form\FormStateInterface;

/**
 * Implements hook_form_node_form_alter().
 */
function uswds_form_node_form_alter(&$form, FormStateInterface $form_state, $form_id) {
  // Make the delete button on node forms pop.
  $form['actions']['delete']['#attributes']['class'][] = 'usa-button';
  $form['actions']['delete']['#attributes']['class'][] = 'usa-button--secondary';
}