How to inherit 'Date' element in webforms? I tried to simply extend the Date element in webforms like this

/**
 * Provides a 'birthday' element.
 *
 * @WebformElement(
 *   id = "birthday",
 *   label = @Translation("Birthday"),
 *   description = @Translation("Provides a custom form element for birthday date selection."),
 *   category = @Translation("Date/time elements"),
 * )
 */
class BirthdayElement extends Date {}


and I see and can select it in the build options. However when I click on the Test tab, I only see the Label and no date input field. What am I missing?
Webform elements require a Drupal Form API 'Element' plugin and 'WebformElement' plugin.

@see webform_example_element.module