Improve CSS and load fonts from https

Some rules borrowed by Bedrock
http://mozweb.readthedocs.org/en/latest/css-style.html

* one rule per line
* lower case for hex colors, short form if possible, don’t use web
color names (some of them are not included in CSS 2 too)
* no quotes in url(), only single quotes
* add Arial as fallback before the default sans-serif font
Merge pull request #322 from flodolo/issue321

Improve CSS and load fonts from https
Reflect changes on languages_all.json