Fix Aphront Filter on mobile

Summary: Some of this CSS causes fake margins on mobile devices. Fixes the margin and widths for consistency.

Test Plan:
Test a number of filter interfaces on iOS, Maniphest, Differential, etc.

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D8959