Threesome , a nice variation of the Set Card game

I'm kind of addicted to the set card game. It is like most games a love/hate relationship. What boggles my mind is that most of the times you find a solution pretty easily and then you get stuck and are really at a loss.
This is a very simple version of it with 15 cards in stead of 12  en it is all made up of css and html code without any image files. Quite an achievement!!
It is very small and you can play it offline as long and as often as you want.
The game is hosted here and is 20 kb small.