I think that you are referring to the actual categories names and as these are 'a'
entries you would have to address these as individual & I think without checking that this will address them directly and replace the 'a' listing for them in the css
a.category-top {
color: #??????;
width: 100%;
margin: 0px 5px 0px 0px;
background-color: #??????;
background-image: url(../images/your_image.gif);
text-decoration: none;
}
And you might do this for:
a.category-top:hover, a.category-subs, a.category-subs:hover etc. and these could provide rollover images. I can't recall if this requires the better categories mod or not right off.
This gets you an Image with the normal text and stays dynamic and for all additions/changes to your listings