Board Thread:Support Requests - Designing Your Wikia/@comment-34167962-20151223003203/@comment-4731443-20151224015735

You can keep the above rule for color and padding, but remove the background property. Set a different rule for each tab with the following: etc. (or, for image+text:) etc.
 * 1) startabber ul.tabbernav li:nth-of-type(1) a { background: transparent url("http://IMAGE-1") no-repeat scroll center center; }
 * 2) startabber ul.tabbernav li:nth-of-type(2) a { background: transparent url("http://IMAGE-2") no-repeat scroll center center; }
 * 1) startabber ul.tabbernav li:nth-of-type(1) a { background: transparent url("http://IMAGE-1") no-repeat scroll 5px / 15px; }
 * 2) startabber ul.tabbernav li:nth-of-type(2) a { background: transparent url("http://IMAGE-2") no-repeat scroll 5px / 15px; }

(Edited to use li:nth-of-type, which should be safer)