node_form_system_themes_admin_form_alter

node_form_system_themes_admin_form_alter(&$form, FormStateInterface $form_state, $form_id)

function node_form_system_themes_admin_form_alter(&$form, FormStateInterface $form_state, $form_id) {
  $form['admin_theme']['use_admin_theme'] = array(
    '#type' => 'checkbox',
    '#title' => t('Use the administration theme when editing or creating content'),
    '#description' => t('Control which roles can "View the administration theme" on the <a href=":permissions">Permissions page</a>.', array(':permissions' => Url::fromRoute('user.admin_permissions')->toString())),
    '#default_value' => \Drupal::configFactory()->getEditable('node.settings')->get('use_admin_theme'),
  );
  $form['#submit'][] = 'node_form_system_themes_admin_form_submit';
}