Summary:
Ref T10054. I haven't done any of the big-picture layout stuff yet, but this should get look-and-feel somewhere in the ballpark of reasonablness, I think.
Major missing stuff:
- No "collapse" state or action yet.
- Menu is not full-height (requires changes to the rendering pipeline).
Test Plan: {F1060941}
Reviewers: chad
Reviewed By: chad
Maniphest Tasks: T10054
Differential Revision: https://secure.phabricator.com/D15016
