Summary:
Ref T7014.
When no devices are connected, we don't meaningfully activate `JX.Scrollbar` (by design), but there was no fallback overflow CSS.
Also massage a couple of other CSS things to get sliiightly less broken behavior.
Test Plan:
- Disconnected USB devices; scrolled.
- Connected USB devices; scrolled.
Reviewers: btrahan, chad
Reviewed By: chad
Subscribers: epriestley
Maniphest Tasks: T7014
Differential Revision: https://secure.phabricator.com/D12008
9ba430cca9