White hover policy icons

Summary: Makes a white hover icon show on the policy dropdown. Also fixed some spacing. Fixes T4017

Test Plan: hover over the policy dropdown

Reviewers: epriestley

Reviewed By: epriestley

CC: Korvin, epriestley, aran

Maniphest Tasks: T4017

Differential Revision: https://secure.phabricator.com/D7388