Forum:Adding Background-image to an Infobox?

I feel really silly asking this, but how do you add a Background-Image to an Infobox? I feel like I've missed something obvious.

I spent a couple hours on the weekend designing (read: trying) a really nice Infobox in Photoshop, but now I can't get it into the Wiki. I'm trying to give the second black box the image:

http://vampirewars.wikia.com/wiki/Template:Infobox_Ability

http://vampirewars.wikia.com/wiki/File:Infobox_Image_Background.jpeg

http://vampirewars.wikia.com/wiki/MediaWiki:Common.css


 * You'll have to use underscores instead of spaces in the url for . Spaces are generally considered to be delimiters for urls.

Okay I've fixed that mistake, but I'm not sure how to apply the class. This doesn't seem to provide the image:

hello world! -Adam weiler 19:26, March 10, 2012 (UTC)