you will also want to scroll a little farther down in the css file and find the:

.leftboxfooter, .rightboxfooter, .centerboxfooter, .singleboxfooter {
background-color: #abbbd3;
background-image: url(../images/tile_back.jpg);
margin-bottom: 15px;
}
and make the same change to get the bottom footer of the sideboxes to match