Feature: support adding a className

[kunukn]

Would you consider adding support for className?

e.g.

<Portal className="my-portal">
  <div>My modal component</div>
</Portal>

Or if this API is not desired, then I could adjust the PR to be like this instead.

const { Portal } = usePortal({ className: 'my-portal' })

<Portal>
  <div>My modal component</div>
</Portal>

[kunukn]

I just noticed there is portalRef. I could use that to add my className. I will use that for now :)

[alex-cory]

This is great and exactly what I was planning on doing. See my milestones issue here.