<!DOCTYPE html>
<html>
<head>
  <style type="text/css">
    .box {
      height: 50px;
      width: 300px;
      margin: 10px;
      background-image: -webkit-linear-gradient(black, black);
      border-radius: 50px;
      border: 4px solid #EEE;
    }
    .transformed {
      -webkit-transform: scale(0.5);
    }
  </style>
</head>
<body>
  <!-- You should see no black leak out of the border. -->
  <div class="box"></div>
  <div class="box transformed"></div>
</body>
</html>