[gizmo]

Hmm strange In Light and lucid I have this:
}
.tabs li {
float: right;
margin: 0px 1px 0px 0px;
padding: 0px;
background: transparent url(images/tab_r.png) no-repeat right top; (Renamed that to find out what's happening)
height: 25px;
}
.tabs a:link,
.tabs a:visited,
.tabs a:hover,
.tabs a:active
{
display: block;
background: transparent url(images/tab_l.png) no-repeat left top; (Renamed that to find out what's happening)
margin: 0px 5px 0px 0px;
padding: 5px 10px 5px 15px;
text-align: center;
vertical-align: middle;
white-space: nowrap;
color: #253161;
text-decoration: none;
font-weight: bold;
font-size: 11px;
height: 25px;
outline-style: none;

After doing that I still had an image appearing on right, went to images and took a look and theres another image > named "tab_r.gif" size 5x25 so I renamed and image gone, that's as far as I have got, but it looks like theres another image for you to modify, well there is in light and Lucid.. (Haven't started looking for css yet, but it's not in main within css) At a guess I bet it's in ie6/7.css as PNG issue

It's a starting point for you.
I was going to work on my custom tabs, and now it's given me a starting point.

Hope this helps in some way.