[jmlucjav]

Anybody has some extension to change colors when background is black and text is white? I don't know if this is common or not, but I just cannot look at that for more than a few seconds, my eyes burn. I never found an extension for Chrome that fixed this.

[ImaCake]

Yes, you want DarkReader which is an extension available on most web browsers. Aside from being able to dark mode websites it has ways to complete customise the background and text colours. I am writing this with high contrast orange text on dark brown background on ios safari.

https://darkreader.org/

[tempodox]

I'm using Reader mode on such sites, but some sites are structured in a way that only part of the text, if any, shows up in the Reader view.

I'm just hoping that sites with a fixed dark-mode design stay the minority because many of those that I've seen are horribly bad and literally hurt my eyes.

[frankfrankfrank]

I’m not totally sure if this fully addresses your issue; but safari reader mode on all devices uses a gray text on black or dark grey backgrounds.