For Categories Dressing, see the sections in the readme titled "To display all top categories as colored boxes:" and "For a "rollover" effect to change the appearance on hovering:".

Change the background: no-repeat; declaration to something like background: url(../images/mycatbg.gif) no-repeat;
and adjust the background: #ddeeff url(../images/catbghover.gif); to whatever you desire.