Overlay: allow changing z-index

[adixon-adobe]

Expected Behaviour

Overlay z-index is changeable via a css custom property

Actual Behaviour

It's hard coded to 1000

[Westbrook]

Could you share a little more about the use case here?

Is the goal to just make it universally different?

Or do you actually have a context where some overlays should be of different z-indexes? In which case, I'm not sure a CSS Custom Property is the sort of API that would make such an API each to consume...

[najikahalsema]

This is something to investigate as we refactor the overlay API, but without an investigation or a repro, it can't be an actionable item at this point.

[Westbrook]

We'll be surfacing --swc-overlay-z-index-base as a custom property to outline the floor of the Overlay stack when AND ONLY WHEN the stack is being delivered in a fallback context. When delivered with the popover API, the popover stack will place content on the Top Layer of the browser, which manages content via a strict stack.