Maniphest mobile CSS tweaks

Summary: Fixes a few minor quirks when viewing maniphest on mobile.

Test Plan: shrink maniphest screen, easier to read.

Reviewers: epriestley

Reviewed By: epriestley

CC: Korvin, epriestley, aran

Differential Revision: https://secure.phabricator.com/D7270
Make UIStatusList background element transparent instead of white

Summary: Fixes T3933.

Test Plan: See screenshot.

Reviewers: chad

Reviewed By: chad

CC: chad, aran

Maniphest Tasks: T3933

Differential Revision: https://secure.phabricator.com/D7272