Only a tiny percentage of websites uses a dark color scheme.
I have a small bookmarklet for nuking colors, which I can run via some shortcut (ShortcutKey2URL).
javascript:for(var e of document.querySelectorAll('*')){e.style.color=window.getDefaultComputedStyle(e).color;e.style.backgroundColor='#fff'}void(0)
Kinda crude but it works well enough.
Presuming your OS has such features, you might find it helpful to invert the screen when looking at pages with light text/dark background.
(I change my screen to normal for such sites.)
HTH