R1:320f7689dda0

Fix Differential DashHeaders

Summary: Adds a basic style to ObjectItemList Headers. Fixes T5465

Test Plan: Added the same Query, tested various layouts

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T5465

Differential Revision: https://secure.phabricator.com/D9711