Dark description tweaks for Pholio.

Summary: Uses a dark description area and white text for pholio mocks. Also touches up the borders a little bit.

Test Plan: review pholio, files, and macros for visual changes intended or not.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D5143