更改上边框的样式 - 在线编辑器

          <!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <title>蜜蜂教程(mifengjc.com)</title>
  <style type="text/css">
    #ex1 {
      border: 1px solid #FF0000;
    }
  </style>
  <script>
    function displayResult() {
      document.getElementById("ex1").style.borderTopStyle = "dotted";
    }
  </script>
</head>
<body>

  <div id="ex1">这是一些文本。</div>
  <br>
  <button type="button" onclick="displayResult()">修改上边框的样式</button>

</body>
</html>
        