Find this in your stylesheet and adjust the highlighted entry to your taste
Code:
A.category-top {
font-family: Arial, Helvetica, sans-serif;
font-size: 12px;
color: #ffffff !important;
width: 100%;
margin: 0px 0px 0px 6px !important;
padding: 0px 0px 0px 10px;
background-image: url(http://www.activatemediainc.com/demo_store/images/new_template_images/button_up.jpg) !important;
background-repeat: no-repeat;
height: 24px;
display: block;
text-decoration: none;
line-height: 24px;
}
Clyde was faster on the draw!!!