Dark prop for popover kit

[patmccler]

Describe the solution you'd like
The popover kit doesn't react when you pass it dark as a prop.
I think it'd make sense to have the background color of the popover change to a dark background.
Maybe the shadow could update as well, but that's less clear to me.

Describe alternatives you've considered
For now, using the white background popover.

Additional context
This came up when implementing the passphrase kit. The kit was designed to use a popover, and a handoff was given to use the passphrase kit on a dark background (here)
At Cole's suggestion, I'm sticking with the white background for now and putting this issue in

Here's an example I hacked together to show the difference

[patmccler]

@coleerikson here's the issue we talked about. Thanks again

[jasoncypret]

Great suggestion @patmccler! We have purposely not moved forward with this on the kit. We are still evaluating if we will be adding it or not. Thanks for bringing this up, but plan on using the light popovers for the time being.