That could be normal for the website. Have you tried using other web browsers?

Is this with all websites/pages, some, a few?

Please provide a public link (no password) that we can check out. No Personal Information Please !

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

Make sure you allow pages to choose their own colors.

• Settings -> General: Fonts & Colors -> Colors: "Override the colors specified by the page with your selections above"

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

As a footnote, here a link to the support article on High Contrast mode: Disable high contrast mode in Firefox.