So when you compare borderradius: 4em 8em to borderradius: 4em / 8em the results are quite different. The symmetrical corners on the left form quarter of a circle, whereas the asymmetrical corners on the right are part of an ellipsis. The shapes that you get with this look a little odd, to be honest. But remember the circles you create with borderradius: 50%. You get a circle because both ...