 `no-cancel-on-esc-key` and the `no-cancel-on-outside-click` properties.
  `close()` should be called explicitly by the implementer when the user interacts with a control
  in the overlay element. When the dialog is canceled, the overlay fires an 'iron-overlay-canceled'
  event. Call `preventDefault` on this event to prevent the overlay from closing.

  ### Positioning

  By default the element is sized and positioned to fit and centered inside the window. You can
  position and size it manually using CSS. 