I definitely didn’t decide, but this is a bit for comment.
The unit does not matter, it is the same as em , cm , ect.
div.box1 { border-radius: 64px; border-bottom-left-radius: 0px; }
It will work (the light bit stretches completely), but adding border-bottom-right-radius will turn it off again.
As soon as one of the border-bottom-XXX-radius gets below 62px , it stops.
I do not know if this will help to find the answer, but I hope it will be.
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