Fix warning panel on large commits

Summary: The warning panel on large commits in diffusion was being overrun with other styles. Fixes T3952

Test Plan: test on a large commit

Reviewers: epriestley

Reviewed By: epriestley

CC: Korvin, epriestley, aran

Maniphest Tasks: T3952

Differential Revision: https://secure.phabricator.com/D7456