I ended up with the following CSS. It's an adaptation from the YUI documentation with trial and errors, might contain very stupid CSS errors but tabs looks like FB tabs.
/* .yui-navset defaults to .yui-navset-top */
.yui-navset .yui-nav,
.yui-navset .yui-navset-top .yui-nav { /* protect nested tabviews from other orientations */
border-color: #d8dfea;
border-style:solid;/* #2647a0; /* color between tab list and content */
border-width:0 0 1px 0;
Xposition:relative;
zoom:1;
padding-left: 4px;
}
.yui-navset .yui-nav li,
.yui-navset .yui-navset-top .yui-nav li {
margin:0 0.16em 0 0; /* space between tabs */
padding: 0px;
zoom:1;
}
.yui-navset .yui-nav .selected,
.yui-navset .yui-navset-top .yui-nav .selected {
margin:0 0.16em -1px 0; /* for overlap */
}
.yui-navset .yui-nav a,
.yui-navset .yui-navset-top .yui-nav a {
background-color:#d8dfea;
border:solid #a3a3a3;
border-width: 0px; /*top right bottom left*/
color:#3b5998;
text-decoration:none;
padding: 4px 8px;
}
.yui-navset .yui-nav a em,
.yui-navset .yui-navset-top .yui-nav a em {
border:solid #a3a3a3;
border-width:1px 0 0;
cursor:hand;
padding:0.25em .75em;
left:0; right: 0; bottom: 0; /* protect from other orientations */
top:-1px; /* for 1px rounded corners */
position:relative;
}
.yui-navset .yui-nav .selected a,
.yui-navset .yui-nav .selected a:focus, /* no focus effect for selected */
.yui-navset .yui-nav .selected a:hover { /* no hover effect for selected */
background-color: #ffffff;
color: #333333;
text-decoration: none;
border-width: 1px 1px 0px 1px;
border-style: solid;
border-color: #d8dfea;
}
.yui-navset .yui-nav a:hover,
.yui-navset .yui-nav a:focus {
background-color: #3b5998;
color: #ffffff;
text-decoration: none;
}
.yui-navset .yui-nav .selected a {
padding: 8px 8px; /* raise selected tab */
}
.yui-navset .yui-nav .selected a,
.yui-navset .yui-nav .selected a em {
border-color: #d8dfea;
/*border-color:#243356; /* selected tab border color */
}
.yui-navset .yui-content {
background-color: #ffffff;/*#edf5ff;/*#D8DFEA;/*#edf5ff; /* content background color */
}
.yui-navset .yui-content,
.yui-navset .yui-navset-top .yui-content {
/*border:0px solid #808080; /* content border */
padding:0.25em 0.5em; /* content padding */
border-bottom-width: 1px;
border-bottom-color: #d8dfea;
border-bottom-style: solid;
}
.yui-navset .yui-content h2 {
background-color: #ffffff; /*#edf5ff;*/
}