corner-shape: round | squircle | bevel | se(v);

where

se(v)

is a superellipse, with the parameter shifted so:

se(0)

is bevel.

se(1)

is round.

se(2)

is a squircle.

se(infinity)

is a square.
All negative values do the same thing but inside the shape.

Some examples: reset pointer diamond cut