Embedded video thumb has been displayed on all overlay windows
You could try CSS z-index Property


  Definition and Usage
  
  The z-index property specifies the stack order of an element.
  
  An element with greater stack order is always in front of an element
  with a lower stack order.
  
  Note: z-index only works on positioned elements (position:absolute,
  position:relative, or position:fixed).


Try setting a higher value to the overlay or a lower value to the youtube player.