How do you avoid being flash-blinded when using the new "Dark Mode" feature of MacOS Mojave?

I turned on Dark Mode, and I liked it a lot, until I switched to my browser window, which of course, had a white page showing, because almost all websites have a white page showing. And because my eyes had adjusted to Dark Mode, I was rather inconveniently blinded for some moments.

They say Dark Mode is supposed to give you relief from bright screens, but there seems to be a cost involved. Or some hoops to jump through. I supposed you could get into the habit of closing your eyes whenever you switch to your browser.

How do you prevent this? Is there some feature I’m missing that darkens webpages?