Try to start reducing Diabook CSS

I've reduced redundant CSS in the base diabook and the diabook-aerith themes by making the -wide variants inherit from the non-wide variants. There should be very little, if any, difference in the theme.

Further improvements could be made by making the -network and -profile base css files inherit from the main style.css file for each theme. Then the base style.css file for each theme could be made to inherit from the high-level base style.css. It's a lot of work.