Update Timeline for Tablet/Mobile
Summary: Minor CSS fixes Fixes T4419
Test Plan: Test phone and table breakpoints, submit a new comment.
Reviewers: epriestley, btrahan
Reviewed By: epriestley
CC: Korvin, epriestley, aran
Maniphest Tasks: T4419
Differential Revision: https://secure.phabricator.com/D8211