I don't think they meant that it would be needed to make new overrides for every site typically. Dark Reader extension works fine with 99% of sites out of the box and is free.

You're right. Someone should do it for you, for free. /s

No, just the ones you really care about.

Caring about the background color of a website is unhealthy and unfair. You have the client-side tools to fix it, so do it.

It's easier than you'd think.

In many cases, you can probably get by with your browser's default Reader Mode.

I'll use uBlock Origin's element zapper on a whole heck of a lot of sites, and you can write default rules for common annoyances as well.

If you get fancy, you can write generalised styles which address specific annoyances, and toggle those on or off on specific websites.

Otherwise, I'd found I'd written a thousand or so custom styles over a couple of years at one point. Most were quite elementary (usually font tweaks or removing headers / social link-litter). A few ... somewhat less elementary. Taught myself a lot about CSS in the process.