#test2 { width: 100px; height: 100px; border-radius: 25px; background-color: rebeccapurple; }
#test2 { width: 100px; height: 100px; border-radius: 50px; background-color: rebeccapurple; }
如果使用百分比,基数就是元素的offsetWidth
#test2 { width: 100px; height: 100px; border-width: 10px; border-color: black; border-radius: 50%; border-style: solid; }