I am going to request the website be changed to use black text. The default light grey is very difficult for many people to read. I have fought vision issues my entire life, and I find most of the text used is very hard to read. At times, I find myself guessing what it says. I have to retype when it is wrong, and hope I get it right. I desired, I do have websites that test for common visual issues that I can give for this purpose. Just let me know if the websites are wanted. Thanks for working so much to bring out a quality web browser.
You are right.
In the meantime you can use Vivaldi's invert filter (look at the small icon < > next to the zoom slider)