If CSS property value is not limited in length, you could actually put the whole browser source code in it... :-)
Starting, of course, with writing CSS in CSS.
(Recently saw a video with one of Thompson or Ritchie, IIRC. He described his mentor defining a language, defining that language in that language, then hand-translating that second definition into machine code. TMG -- transmogrifier.)
What we REALLY need here is to be able to compile CSS into x86 so you can write a multi-threaded kernel for your CSS-coded browser to run on.