You should leave that up! No doubt someone else will be looking for that, how about a mini tutorial on it? I couldn't find anything describing how to do it anywhere searching! Great work!
Hey, you should probably use jayjdk's solution unless you're using border-radius.
What I did:
I added an empty span to the outer container. The outer container is relative positioned, and the span is absolutely positioned inside, width a width and height of 100%. Then since the span and the container are now of the same dimensions, you can apply outset to one, and inset to the other. Problem solved