in styles.php du kannst folgendes andern
.sideblockheading {
/* background-image: url(<?PHP echo "$themeurl"?>/gradient.jpg); */
background: rgb(0, 0, 128); <---
border-width: 0px 2px 0px 0px;
border-style: solid;
border-color: rgb(104,104,104) white;
color: white;<---
font-weight: bold;
padding-left: 8px;
}