Why does Zen Browser change the appearance of some sites?

[DogeYT4101]

Hello! I'd like to know how to disable the feature that removes the background of some sites like Pinterest and Classroom. It's really annoying and doesn't go well with the color of the text.

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P.S.: The site's language is Portuguese, don't mind it lol

[DavitMunjishvili]

Can you check browser.tabs.allow_transparent_browser in about:config?
If it's true, try changing it to false and reopening tabs.