Question 1

What's the difference between single and elliptical radii?

Accepted Answer

A single value like 20px makes a perfectly round corner. A pair like 20px 40px produces an elliptical corner — 20px horizontal curve and 40px vertical curve. Toggle the Elliptical mode to expose both.

Question 2

Can I use percentages?

Accepted Answer

Yes. Switch the unit selector from px to % and your radius is computed relative to the element's box. 50/50% on a square makes a perfect circle.

Border Radius Generator