<!DOCTYPE html>
<!--
 | Setting all borders with a radius but only one edge with solid color and width.
 |   https://www.w3.org/TR/css-backgrounds-3/#border-radius
 -->
<html>
<head>
  <style>
    div {
      border-left: 20px solid blue;
      border-radius: 10px;
      height: 100px;
      width: 200px;
    }
  </style>
</head>
<body>
  <div></div>
</body>
</html>