3809: shorten TOS box

TOS box was very big. Made it 36em.

Wasn't sure whether to do this in one of the CSS files, so I ended up amending app/views/uers/_legal.html.erb and putting the CSS there. Perhaps that was entirely wrong... /newcoder

https://code.google.com/p/otwarchive/issues/detail?id=3809&q=Difficulty%3DEasy%20status%3DAccepted%20component%3DFrontEnd&colspec=ID%20Roadmap%20Type%20Status%20Release%20Milestone%20Owner%20Component%20Priority%20Summary