css linted: selector performance improvement

I linted the css files with cssLint and adjusted the selectors to make them faster. I tested the changed stylesheet and I think we got some performance improvement. I was pretty radical, so I can't say for sure that I didn't broke anything, but everything looked fine to me.
plus menu fix
Merge pull request #593 from TitanNano/csslint

 css linted: selector performance improvement