It's now possible to follow the OS dark mode preference in CSS. 🌝🌚

Stackoverflow is using it and it's brilliant [1].
It seems that now it is reasonably simple and supported [2] using CSS.
This would require a new option where one defines the dark and light themes one wants and then MM uses the CSS tech above to switch them under the hood.

[1] https://stackoverflow.blog/2020/03/31/building-dark-mode-on-stack-overflow/
[2] https://stackoverflow.com/questions/50840168/how-to-detect-if-the-os-is-in-dark-mode-in-browsers