User blog comment:Dopp/Technical Update: July 26, 2011/@comment-2093602-20110727142540

For wiki's that already had a transparent background (through a transparent image), you can keep using that image by adding something like this to your CSS: .WikiaPage .WikiaPageBackground { background: transparent !important; }  may also work. This will hide the background added by the theme designer (which sits on another div for some reason).

Of course you can also choose to remove the background image and use the new Theme Designer method (through CSS opacity, which only works in recent browsers) instead.