WTH is there no documented list of themeable elements?

I realise that themes are in a bit of a state of flux at the moment but a list of themeable elements (and a short description for each) really would aid in fronend customisation.

Ditto that…

I have to edit some element I find online and reboot to see if I can find what it changes. A simple list of what “scrollbar-thumb-color” actually changes would be awfully handy.