Use standard icon size, color on mobile headers

Summary: This just matches the UI of icons on mobile with the icons size, color on desktop.

Test Plan:
test tablet and phone breakpoints.

{F369688}

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D12407