There's no code, it's only a collection of themes based on a "standard" template.
The CoffeeScript code you see is for the bookmarklet used on the playground. It is old code, coded in a rush, most for proof-of-concept. I'm slowly rethinking this playground and theme development stuff, so this is going to be replaced.
The only thing I'd suggest is, use ES6 instead of CoffeeScript or provide an ES5 copy of the code.