[throw5345346]

https://fullsiteediting.com/themes/ has a list, including one or two skeletons.

I am tempted by Anders Norén's Björk, which is also FSE:

https://andersnoren.se/teman/bjork-wordpress-theme/

I think I did most of my learning with Carolina's own Jace theme.

(FWIW I have always thought the roots.io stuff is a mistake, conceptually.)