How to set dark theme

I'd like to use a dark theme (eg. dark body background, light text colors) and I assume there's some simple way to define this in a custom sass, but I can't figure out how.

I was able to override variables, eg. override `$body-bg` in my custom.scss (also modifying `package.json` and `docs.scss` to use/import my `custom.scss` so I could also see the rebuilt docs reflect my color changes, but of course this is just cherry-picking `$body-bg`...

Am I wrong assuming there is an easy way to swich from light to dark easily?