Like ad blockers, sometimes you have to adjust it, but it usually Just Works. The main innovation from this is that my display has much improved contrast, because I can set the brightness for text on a black background, instead of setting the brightness for an entire screen of white. It is amazing how good a screen looks when it's not running at 1% brightness. (Just don't open a non dark mode app at night, or you won't be sleeping for a week.)
I'm not 100% certain that this should be forced by the browser and IMHO it's the websites owners job to provide properly working dark theme and the UI/UE they think fits best their purpose (and not the browsers). Unless the assumption is that styling across all sites should look 100% identical which may appeal to some, though if I really want that then I can go look for content on gemini:// and no page will ever use their own styling other than what I am telling it to. Maybe it's just me but I like being dazzled and surprised with new design and style that I've not seen before.
I agree that all websites should give users a dark mode. They don't, so we have to make our own.
And for $4.99 Safari user. 30% paid to Apple and 70% for developer to recoup their $99/year cost.
Does it add something to the satire, or does it make it funnier? Clearly the original page's lack of a license didn't make it impossible for anyone else to iterate on it.
And again, I can't stress this enough, the point of the original page was not that every single addition you could make to a website was bad. It was not that you shouldn't have a dark mode. It used radical minimalism to show that by default websites work, even if you have no clue what you're doing.
The lack of niceties is the point. Nobody was unable to read the original page or iterate on it. Could the page have been nicer? Sure. But the point was that even if you did nothing at all, the web still worked.
So it's appropriate in this context, but also pretty easy to argue that 10 lines of code are not a serious copyright threat anyway, and that it's not clear what code on this page is even subject to copyright in the first place, and that the author might have gone all the way and leaned into the fact that you don't really need an entire Git repo with a license for a single HTML page.