On a related note: today I learned it’s super easy to give your website an alternate dark mode theme in most browsers. Assuming your color scheme is in relatively clean CSS to start with, anyway.
Just add a @media (prefers-color-scheme: dark) {…} section after you define the light-scheme colors and define the dark mode colors and backgrounds there!
https://developer.mozilla.org/en-US/docs/Web/CSS/@media/prefers-color-scheme