border-radius:

border-radius order: (top left)(top right)(bottom right)(bottom left)

1

2

3

4

Box1 round: border-radius: 100px;

Box2 corners: border-radius: 20px;

Box3 warp: border-radius: 20px 10px 190px 10px

Box4 warp: border-radius: 20px 20px 100px 100px

If all corners have the same number you can write it with one number such as
border-radius: 20px; for a short hand version

border-radius: 20px;
is equivalent to writing:

border-top-left-radius: 20px;
border-top-right-radius: 20px;
border-bottom-right-radius: 20px;
border-bottom-left-radius: 20px;