Hygiene: Fixing formatting of Special:Uploads

The correct margin CSS for .content is already provided elsewhere:
  content/main.less (phone)
  tablet/common.less (tablet and desktop)

Also changing padding to em value (same rendering).

Also getting rid of gray background in phone view per design.

Change-Id: Id3249df13ce31c165c5ed7a7ea9b7cfe58caa950
Merge "Hygiene: Fixing formatting of Special:Uploads"