Change images:
/skin1/images/toptab_bg.gif
/skin1/images/toptab_bg_hover.gif
PHP Code:
/*
Tab mechanism
*/
.Tab { padding-bottom: 3px; padding-top: 3px; color: #fff; font-size: 10px; text-transform: uppercase; }
.Tab a { border-left: 1px solid #000; padding: 3px 8px 3px 8px; background: url('images/toptab_bg.gif') repeat-x bottom; color: #fff; text-decoration: none; }
.Tab a:hover { padding-bottom: 3px; padding-top: 3px; background: url('images/toptab_bg_hover.gif') repeat-x bottom; color: #fff; text-decoration: none;
PS. The decision to use " " - not very beautiful in top menu.