Pulling out this commit from #30778 which is outdated and kind of a mess.
- bg-gray is new and maps to gray-400
- border-gray-500 and border-gray-700 are new and are meant to complement bg-gray and bg-secondary as one level off from the borders
Still TBD if we want it, but figured I'd separate this out for now to see if we want/need it.
Preview: