[Redesign] Minor mobile CSS updates

Summary: Ref T8099, Lots of little mobile tweaks browsing around.

Test Plan: Look everywhere, for things, and stuff. Then align it better.

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T8099

Differential Revision: https://secure.phabricator.com/D13037