I understand that the "em" measurement is a relative unit for font-size, relative to the font-size of the containing element if it's specified in an absolute unit like px, or to the default font-size in the browser.
But I'm trying to understand how using em as a measurement for the border-radius of a box element, like a div, works. I'm assuming it's related to how using em as a measurement for the width or height of a box works.
Is it still related to font-size? How, specifically, is it measured? The explanations for how border-radius is computed that I've been able to find all seem to be based on px units.