Add and remove a class when you select a tab link..
#navigation .active {
color: #000;
background: -webkit-gradient(linear, left top, left bottom, from(#DFE7FA), to(#FFF));
border-bottom-width:0px;
}
and use the script (jQuery version)
$(function(){
$('#navigation a').click(function(){
$('#navigation .active').removeClass('active'); // remove the class from the currently selected
$(this).addClass('active'); // add the class to the newly clicked link
});
});