This is really well done, thank you!

Is it possible to make the font configurable? That can be done in the header like:

@var select user-font "Font" ["Comic Sans MS", "Comic Neue", "PT Sans", "PT Serif"]

Then later use it like:

html {
    font-family: var(--user-font);
}

Full working example at my Discord Solarized Dark Comic Sans MS theme.