Problem

According to the documentation, you either have to stick with the shipped themes or swap them out entirely/modifying them.

I would like to keep the default themes, but only add extra ones alongside them.

I would like to be able to easily make simple color alterations without having to go through the entire swamp of CSS.

I would like to be able to just find themes other people have shared and paste them into the direction and have it automatically show up in the dropdown selector of the compiled book

Proposed Solution

An entrypoint like Jekyll does with custom-variables would be neat, this way users don't need to deal with the entire CSS when all they want is a slightly altered color scheme.

Have the existing theme files be just a folder of stylesheets. Adding or removing them from the directory automatically changes the resulting dropdown listing to match what's in the folder.

Or perhaps something similar to SUMMARY.md but instead it's THEMES.md where you list out theme entries and their respective references.

Or some other ways of implementing that is ergonomic to the use case of "ok, it ships with these five themes, I want to remove two of the light ones, and add three of my own that is just a slight color tweak of Navy, without having to write an entire CSS sheet for every element"

Notes

No response