Respect the user prefers-color-scheme

[kafran]

Summary

Hello Michael. Thank you for this awesome theme.
Since the theme already has white/dark themes available I would like to suggest to add the support for prefers-color-scheme to change the theme according to the user browser preference for white or dark theme. A nice example of the feature is the docker documentation https://docs.docker.com/ which will change automatically to white/dark according to the user preference, the portal even has a switcher for the user to change between dark/white modes.

https://developer.mozilla.org/en-US/docs/Web/CSS/@media/prefers-color-scheme