empires: Defer to top-level style sheet for as much as possible

empires: Defer to top-level style sheet for as much as possible

Most of the top-level lmno style.css was originally copied from the
style.css file from empires-html in the first place. So there was a
lot od fuplication in these files.

In this commit, we reference the top-level style.css from the empires
HTML file and drop from the empires style.css file all directives that
already exist above.