In WordPress Twenty Eleven Theme if you place a You Tube video directly below the main navigation, any sub nav menu will disappear behind the video not in front of it.

To correct this behaviour you need to add an attribute to the embed or iframe code

1. add wmode=”opaque” in the object tag so the tag resembles:

<object width=”600″ height=”371″ wmode=”opaque”>

<embed src="http://www.youtube.com/VcEo?version=3&amp;hl=en_US&amp;rel=0" type="application/x-shockwave-flash" width="600" height="371" allowscriptaccess="always" allowfullscreen="true" wmode="opaque"></embed>

 

Now your menu should be over the You Tube video.