Minor Differential CSS tweaks

Summary: Fixes notices, uses standard colors for TODOs. Mutes comments just a hair.

Test Plan: Will test on epriestley. Also Differentail and Diffusion.

Reviewers: epriestley

Reviewed By: epriestley

CC: Korvin, epriestley, aran

Maniphest Tasks: T3952

Differential Revision: https://secure.phabricator.com/D7311