Fix CSS for hiding content

:not() only works with simple selectors, not composite selectors.
This caused problems for people with customized skins.
Also, this way we only require support for > (wider) instead of
support for :not.

Also fixed footer id and added monobook for good measure.

Bug: 66326
Change-Id: Ibaa0861aff711723dd336eeaa8c12e73110b1c3b
Merge "Fix CSS for hiding content"