Good simple, but functional design here Daniel. Nice work!
I do think that the "Unavailable cursor should flash or something to help make it seem more "warning-ish." The fact that the resise arrows point inward as opposed to outward feels a little off as well, but it is not bad enough to lose a star, and is simply defies the norm, it's not non-functional because of it.
I do feel a little inspired because of it though. nice job!