<!DOCTYPE html>

<html>
<head>
  <style>
    div {
      width: 300px;
      height: 300px;
      border: 2px solid red;
      border-image: linear-gradient(30deg, black, white) 1 fill repeat;
    }
      
  </style>
</head>
<body>
  <div>
  </div>
</body>
</html>