Thanks Paul, that's exactly what I was looking for. I tweaked your code a bit in order to get the angle on the bottom rather than the sides (see below).
It works great, however, the color of the border is hardcoded into the css. Is there any way to use a color gif image for the background (or via generated content) and manipulate its borders to achieve a similar effect?
border-top: 700px solid rgba(0, 204, 255, 0.5);
border-left: 1950px solid transparent;