I have to admit I'm stumped. The code is there in your stylesheet, and I can't find anything after it that should override it, except
.centerColumn, #bannerOne, #bannerTwo, #bannerThree, #bannerFour, #bannerFive, #bannerSix {
padding: 0.8em;
}
which does not conflict and is already accounted for in my code.
When I look at the page, I see no border/header, but as soon as I hit Edit CSS, the border and header appear just as they should. There is a bug in Web Developer Edit CSS that causes background images to disappear while editing, so I would think that some background that normally appears on top of this border vanishes, allowing it to be visible; however, I can't find any such thing in the stylesheet.
Just for laughs, what happens if you move the code to the very end of your stylesheet?