mkdocs: add light/dark mode toggle

[aSemy]

Adds a light/dark mode toggle to the docs

Live example: https://asemy.github.io/sqldelight/

Documentation here: https://squidfunk.github.io/mkdocs-material/setup/changing-the-colors/#color-palette-toggle

Example config here: https://github.com/squidfunk/mkdocs-material/blob/2569d4f0884b9fe3be934215ce0cfddf8efc94b8/mkdocs.yml#L60-L72

[aSemy]

This change means the header colour dynamically changes between light/dark mode

Before the colour of headers is hardcoded to be grey, even in dark mode:

After, using the var, the colour will dynamically change:

The full set of css vars that mkdocs provide are available here: https://github.com/squidfunk/mkdocs-material/blob/2569d4f0884b9fe3be934215ce0cfddf8efc94b8/src/assets/stylesheets/main/_colors.scss

[hfhbd]

Nice

[hfhbd]

Is it possible to use the media query to auto-switch to light/dark mode? Don't know, if other people would want this behavior too.

[aSemy]

Is it possible to use the media query to auto-switch to light/dark mode? Don't know, if other people would want this behavior too.

The settings in this PR should evaluate the browser preferences to select the correct mode https://squidfunk.github.io/mkdocs-material/setup/changing-the-colors/#system-preference

If you're asking about auto-switching based on time-of-day, the docs say that's not a publically available feature yet

[hfhbd]

Yes, I mean this nice but private feature. But I am fine with the current publicly available feature.