In my version of firefox it renders without the css centering, then centers, then makes my browser stop responding, then gives a blank page.

Nice. This is pretty similar to Mathematica's user interface functionality and Dynamic mechanism:

http://reference.wolfram.com/language/ref/Dynamic.html

http://reference.wolfram.com/language/ref/Manipulate.html

This could be useful for creating notebooks without using Jupyter. If it works, that is. I'm only seeing a blank page.