Those gradient bars are made with an image, tile_back.gif, and you can copy it into a graphics program like Photoshop and change it however you wish.

The sideboxes also have a thick green border at the bottom, which you can change in your stylesheet. Find
Code:
.leftBoxContainer, .rightBoxContainer {
	margin: 0em;
	border: 1px solid #9a9a9a;
	border-bottom: 5px solid #336633;
	margin-top: 1.5em;
	}
and edit border-bottom as desired.