Browsers are starting to allow passing user preference request headers to the server, if the server asks for them.

For example:

Accept-CH: Sec-CH-Prefers-Color-Scheme

...will ask the browser to forward the user's preferred color scheme: light or dark.

This is really useful for providing the correct color scheme styles from the user, without having to do it on the client (a potentially causing a flash of the wrong color scheme).

Just get the color scheme (at the server):

const systemPreferredColorScheme = request.headers.get(

...and serve the corresponding styles.

See more here.