Challenge Add Rounded Corners With A Border Radius - ashish9342/FreeCodeCamp GitHub Wiki
To make round corners it is all about border-radius and pixels.
You can specify a border-radius with pixels. This will affect how rounded the corners are.
.thick-green-border {
border-color: green;
border-width: 10px;
border-style: solid;
border-radius: 10px;
}