There's no Preferences button. If there is, they've either hidden it well, or it's not visible without a login.
There should simply be a button -- a conspicuous one -- that toggles the color scheme. It's trivial to add such a button. It doesn't need to be tied to a user ID; it doesn't even need to set a cookie. The fact that no such button exists is a choice someone made, a poor choice that disregards decades of human-machine interface research.
Failure to go full Karen about goofy things like this has made the Web a little worse for almost everyone in one way or another. So... there ya go.
It's the link in the article. But I'm diverting the thread at this point and arguably making this a worse place by doing so. The other replies indicate that the question has been raised and is under consideration, which is all I can ask given that I'm not prepared to jump on Github and send them a PR myself. Thanks for your reply and the rest of the input people have offered!
There should simply be a button -- a conspicuous one -- that toggles the color scheme. It's trivial to add such a button. It doesn't need to be tied to a user ID; it doesn't even need to set a cookie. The fact that no such button exists is a choice someone made, a poor choice that disregards decades of human-machine interface research.
Failure to go full Karen about goofy things like this has made the Web a little worse for almost everyone in one way or another. So... there ya go.