R1:004a8de35067

Notications mobile menu

Summary: Adding CSS so the notifications menu renders over content on mobile, also it was sort of broken at some point.

Test Plan: Tested Mobile, Tablet and regular layouts.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D5424