What is the purpose of the theme builder?

[yahiakala]

I'm trying to better understand this repo so I can use docker to run apps on my server. I don't see a theme builder in the anvil-runtime repo or configuration. What does the theme builder do for amoni and why is it needed?

[meatballs]

It was an early attempt to allow you to write modular css across multiple files which would then be compiled into a single theme.css.

It's probably now redundant with the advent of dependency based themes.