I feel like you did a good job showing examples as well as defining the radius, but I don't know from reading why we get the shapes we do from the radius. How does this number get applied to the corners of our elements? Why does 50% on a square element, turn it into a circle? I'm not trying to be critical of your post, these were just answers I was hoping to find as I read through.
Thank. I was thinking of integrating it!
There is this wonderful StackOverflow answer how it is calculated:
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