Why does border-radius work incorrectly (cut corners)?

Question

css

Let's look at the screenshot.
I deliberately made the border-radius bigger for clarity. For some reason, it cuts corners (makes them white), while right on the same site in the same menu there are elements that are displayed as they should - without the cropping effect (marked with a green arrow).
I have been tormenting myself with this menu for an hour, but I still have not learned the nature of this phenomenon.

Answer 1

Add to the container overflow: hiddenbecause nested elements have a background color.