I can create a ve.ui.Surface.css file for Wikia and move this selector there. z-index=1 will fix the problem with the #WikiaPage element, but not for .Wikia-video-play-button with its z-index=100. Setting the local overlay to z-index=100 would work, but I wonder other z-indexed Wikia-created or Wikia user-created elements we'll find. It might be best to just set it to a very high z-index now.