 `iron-overlay` opens.
  * @event iron-overlay-opened
  */

  /**
  * Fired when the `iron-overlay` is canceled, but before it is closed.
  * Cancel the event to prevent the `iron-overlay` from closing.
  * @event iron-overlay-canceled
  * @param {Event} event The closing of the `iron-overlay` can be prevented
  * by calling `event.preventDefault()`. The `event.detail` is the original event that originated
  * the canceling (e.g. ESC keyboard event or click event outside the `iron-overlay`).
  */

  /**
  *