Guessing it’s reading the system color scheme, because on my phone it’s white text on black.

(on iOS with dark mode enabled system wide)

For me it’s Dark Reader (https://github.com/darkreader/darkreader) which can be installed on at least chrome and Firefox desktop browsers, and safari and Kagi on iPhones.

I use it to keep from getting flashbanged by my monitor. In this case it also fixes the above site, however some websites need the color filter mode changed to work better, so realistically I’m not ending up with less fixing of websites, just easier fixing.

I tweaked the css in my browser with developer tools.

It’s white text on black bg for me. But to answer your question- reader mode!