MediaWiki:Common.css

ul.tabbernav li a { border:none !important; background: #f0f0f0 !important; font-size: 12px !important; color: #444444 !important; font-weight: 300 !important; margin:3px !important; padding:2px 12px !important; font-size: 13px !important; cursor:default; } ul.tabbernav li:first-child a { border-top-left-radius: 0px; border-bottom-left-radius: 0px; } ul.tabbernav li:last-of-type a { border-top-right-radius: 0px; border-bottom-right-radius: 0px; } .tabberlive .tabbertab { border: none !important; border-radius: 3px !important; padding:10px 10px 5px 10px !important; } ul.tabbernav { background: transparent; border-bottom: 0 !important; padding: 3px 0 !important; text-align:center; margin: 0 0 -10px 0 !important; } ul.tabbernav li a:active { background: #cccccc !important; } ul.tabbernav li.tabberactive a { background:skyblue !important; color:white !important; } ul.tabbernav li.tabberactive a:active { background:skyblue !important; color:white !important; }

Theme 2 - OS X Yosemite Tabber Style result