Theme development just for fun and kill time

Okay... So I now have to much time on my hands and a rooted device with CM13 and TWRP 3.0.2-0 and was thinking of making some skins for TWRP and for CM13.

Is there some one the can point my to a site or post with some info on how I start on that?

Sent from my HTC One A9 using XDA-Developers mobile app