Why would you prefer this over, as another commenter already pointed out, a web standard like the CSS `prefers-color-scheme` media feature? A web feature like that works across websites, is better equipped to deal with user accessibility issues, and doesn't require Javascript.
The use case is different, the standard CSS `prefers-color-scheme` media feature changes the styles according to your system preferences. Here, the goal is to offer to the developer a simple API to create a customizable darkmode feature. I've just started writing this API but I intend to make it more customizable by including `prefers-color-scheme` option and timestamps based darkmode.
Sometimes sites using the dark mode preference are annoying. Usually they just slap white text on dark background which is utterly unreadable for me for blocks of text.
I like to use dark schemes for coding because I get access to more colors and the lines are short and spaced. But for reading a paragraph more than just changing the text color is needed, and none of the sites does that.
So the sites having it toggleable would actually be quite cool. I hope browsers will get a possibility to check/uncheck this per-site.
