feat: add supporting pane to labs

[VandeurenGlenn]

Initial supporting pane support.

@asyncLiz not sure about the mediaqueries if they should be included.

[asyncliz]

Full disclosure, this may not be possible to review right now :(

[VandeurenGlenn]

Full disclosure, this may not be possible to review right now :(

Ah I thought the discussion as the one on chat 😬