CSS - Another one of those "Oops, this shouldn't be happening" questions

CSS - Another one of those "Oops, this shouldn't be happening" questions

I've been building this site in CSS with virtually no problems, and now
all in a sudden I'm experiencing a problem with some basic positioning
that I can't figure out in my body-3 class div, going below my body-4
class div instead of pushing it downward and lengthening the page like
normal. The page almost seems to have some sort of max length, although I
don't believe I've set any sort of max page height.
.body-3
{
/* what's going on here?*/
if you query this on the testing area of the company website that I am
working on right now, in the external css file, you'll see exactly what
I'm talking about.
This testing page is live here:
www.testing.agcomputers.net
Note: that black box appears to be within the body-4 class div (light grey
area at bottom) but they are actually contained within the .body-3 class
div, and have no upper margin that should push them down into any other
div.
I'm unable to choose an answer without enough karma, but these guys below
have found my obvious mistake, where I forgot to close some divs. Thanks
guys!