Admin Forum:How to put a background on Wiki-Navigation

I want my Wiki to have a wiki-navigation background like this Mario Wiki: How to put a background on my wiki-nav??? --Rodel.belmonte (talk) 14:42, February 15, 2013 (UTC) :You must edit the MediaWiki page Wikia.css, and insert this CSS: .WikiHeader { background-image: url(http://url); }
 * At "http://url" you must insert the URL of the image saved in a Wiki.  SuperMarioThree  (Contattami)  15:26, February 15, 2013 (UTC)
 * But, what is the image size?? --Rodel.belmonte (talk) 06:56, February 17, 2013 (UTC)