Mobile CSS fixies.

Summary: Fixing some of my own issues, but also consolidated menu styles and enlarged the search box.

Test Plan: iOS and Chrome, checked core menu and app menu (config).

Reviewers: epriestley, btrahan

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2426

Differential Revision: https://secure.phabricator.com/D4681