Summary:
Warning boxes in a haunted differential comment panel were showing up
without a background (so the contents below were showing through).
This adds the background.
Test Plan:
viewed haunted differential comment panel on a diff with lint errors
and selected "accept revision". Confirmed that the diff and sidebar did
not show through underneath the red warning box.
Reviewers: epriestley, chad
Reviewed By: epriestley
CC: aran, Korvin
Differential Revision: https://secure.phabricator.com/D4154
5cb0f47761