Documentation for creating custom themes

[retreaduntamed]

Hi - could you publish additional documentation on creating custom site themes for those with react knowledge? I believe this is where the book-theme code lives? Unfortunately there isn't much to go on regarding theme development. Appreciate the work on this project.

Referencing this comment from @rowanc1 in this discussion

We don't have that style of theme out of the box, no. Right now there are two supported themes: the article-theme and the book-theme. However, there are also ways to create completely custom themes, but they do require knowledge of react. If that is something that you are interested in we can provide improved documentation for how to get started on your own.