Different visual identities for sections of the website

This might help people not to get lost in our gigantic website, and know easily if they are in the ‘contribute’ section or the ‘documentation’ one for example.

This was decided during the “How to get more contributors” discussion at the 2013 summit.

Related issues

• Related to #7627
• Blocked by #11162 (closed)

Original created by @bertagaz on 6170 (Redmine)