Since I posted the original 3D CSS Box Model diagram, I’ve had a lot of requests from people who want to re-use and/or adapt it. I always intended that it be free for the taking if someone found it useful, but people seem to like the security of a legal document. So its now released under a Creative Commons license to do with as you wish.
Also, as Dunstan pointed out to me, the content is actually on top the of the border, rather than underneath it. You have to do some negative margin tom-foolery to see this, but I’ve updated the original diagram to take this into account.