The TV Tropes wiki has managed to have a built in dark mode for at least the last 7 years. TV Tropes. Come on, guys.
It’d be kind of interesting to have a “dark mode spider” that crawls the Web and checks to see what percentage of websites support the browser-requested dark mode. I’d be kind of curious to see how far along we are.
I mean, people have done it for stuff like IPv6 support for a while.