Question 1

What radius should a nested box use?

Accepted Answer

The inner radius should equal the outer radius minus the padding between them. Otherwise the corners aren't concentric and the eye reads it as wrong.

Question 2

For a pill shape, 9999px or 50%?

Accepted Answer

For a pill button use a large pixel value (9999px); with 50% the corners turn elliptical as the box widens and the shape distorts.

Border Radius Generator