Just FYI... I found an extension called DarkReader that does really well with tough sites..
https://chrome.google.com/webstore/detail/dark-reader/eimadpbcbfnmbkopoojfekhnkhdbieeh?utm_source=chrome-ntp-icon
With the forum theme set to "default" and DarkReader:
b62076f0-3f7d-4682-b648-21d48e2749da-image.png
Oddly enough, I also just discovered that you can copy a screenshot to the clipboard and simply paste it into the forum edit box without saving it to a file first. 🙂