Defines the radius of the top left corner.
default
border-top-left-radius: 0;
Removes any border radius.
border-top-left-radius: 20px;
You can use pixel values.
border-top-left-radius: 50%;
You can use percentage values. In this example, the radius starts halfway on the top border, and ends halfway on the left border.
border-top-left-radius: 20px 50%;
If you set two values, the first one is for the top border, the second one for the left border.