The z-index a body-portaled popover should use so it sits above both the shared floating layer and any outranking surface it was opened from within.
the surrounding surface z-index from useSurfaceZIndex (0 when there is none).
0
POPOVER_Z_INDEX outside any outranking surface, else one above it.
POPOVER_Z_INDEX
The z-index a body-portaled popover should use so it sits above both the shared floating layer and any outranking surface it was opened from within.