As soon as I switched my Mac to dark mode, I immediately began to hate all the white on web sites. It is glaring to see so much white on web sites, when everything else on your computer is dark. Some web sites, switch from bright to dark when they detect dark mode, but most have done nothing about it. So it turns to web browser plug ins fill in the gap. Unfortunately most do not work well.
My favorite is the free open source Dark Reader. It is available for Chrome, Firefox, Safari and Edge, though strangely costs $5.99 for safari, and doesn’t work quite the same with the site list, though it still does the conversion of pages just as well.
The plug in gives you options to change your settings on a site by site basis.
And you can keeps sites from being affected or set individual sites to work. It is a great plug in and works the best of any dark mode I have seen and it doesn’t send your user’s data anywhere.