You've just made it the background itself green, using "#008000" . If you wanted it black like the picture, it was stated that black is "#000000". Also, that border-bottom declaration is wrong. Check other border-bottoms(like for the HR selector) to see where you went wrong.

If you want... simply adjust the padding, you will be able to tuck the image back in without having that bleed line showing.

Try this;

Code:
#navMainWrapper, #navSuppWrapper, #navCatTabsWrapper {
	margin: 0em;
	background-color: #000000;
	background-image: url(../images/tile_back.gif);
	padding: 0.3em 0.2em;
	font-weight: bold;
	color: #ffffff;
	height: 1%;
	}