Also ...

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You can see that page here: https://webmasters.stackexchange.com/questions/132497/getting-html-includes-to-work-with-xampp

The bottom page you can see here: https://shamar.org/articles/word-study-nephesh.html

The top web page image is from: https://webmasters.stackexchange.com/questions/132497/getting-html-includes-to-work-with-xampp

Another examples is: https://kowalczyk.me/change-default-kernel-in-ubuntu-18-04/ All the code has a deep dark grey background.

Make sure you haven't enabled a High Contrast theme in the OS settings.

Make sure you allow pages to choose their own colors.

• Options/Preferences -> General: Fonts & Colors -> Colors: "Override the colors specified by the page with my selections above"

Try "Never" if the default "Only with High Contrast themes" isn't working.

Also check the default colors that are used when a webpage doesn't specify their own colors.

It didn't work.

Anyone?

Got it! It was an add-on "Font Contrast". Disabled it and everything is fine.