Make timeline view prettier
Summary: Aligns the timeline view more closely with the diff_full_view.png mock.
Test Plan:
Desktop:
{F26822}
Mobile:
{F26823}
Reviewers: chad, btrahan
Reviewed By: chad
CC: aran
Maniphest Tasks: T2104
Differential Revision: https://secure.phabricator.com/D4137