trait YamlFormToggleTrait in YAML Form 8

trait YamlFormToggleTrait {

  /**
   * {@inheritdoc}
   */
  public function getTranslatableProperties() {
    return array_merge(parent::getTranslatableProperties(), [
      'on_text',
      'off_text',
    ]);
  }

  /**
   * {@inheritdoc}
   */
  public function form(array $form, FormStateInterface $form_state) {
    $form = parent::form($form, $form_state);
    $form['toggle'] = [
      '#type' => 'fieldset',
      '#title' => $this
        ->t('toggle settings'),
    ];
    $form['toggle']['toggle_theme'] = [
      '#type' => 'select',
      '#title' => $this
        ->t('Toggle theme'),
      '#options' => [
        'light' => $this
          ->t('Light'),
        'dark' => $this
          ->t('Dark'),
        'iphone' => $this
          ->t('iPhone'),
        'modern' => $this
          ->t('Modern'),
        'soft' => $this
          ->t('Soft'),
      ],
      '#required' => TRUE,
    ];
    $form['toggle']['toggle_size'] = [
      '#type' => 'select',
      '#title' => $this
        ->t('Toggle size'),
      '#options' => [
        'small' => $this
          ->t('Small (@size)', [
          '@size' => '16px',
        ]),
        'medium' => $this
          ->t('Medium (@size)', [
          '@size' => '24px',
        ]),
        'large' => $this
          ->t('Large (@size)', [
          '@size' => '32px',
        ]),
      ],
      '#required' => TRUE,
    ];
    $form['toggle']['on_text'] = [
      '#type' => 'textfield',
      '#title' => $this
        ->t('Toggle on text'),
    ];
    $form['toggle']['off_text'] = [
      '#type' => 'textfield',
      '#title' => $this
        ->t('Toggle off text'),
    ];
    return $form;
  }

}