When you go to your dashboard to change your theme...what other secret/hidden themes are and how does one find them?

There are three, all attached to achievements. Luminaire for freeing 1000 snow fairies, Autumn for throwing 1000 items into the bonfire at Fireside, and Morostide for carving 500 pumpkins

Wow, been here for well over 14 years, had no idea! :D Thanks :)