index2.html（position:fixed）

3-6 index2.html（position:fixed）

<!DOCTYPE html>
<html lang="zh-TW">
  <head>
    <meta charset="utf-8">
    <title>position 練習</title>
    <style type="text/css">
    #a {
      width:100px;
      height:100px;
      border:1px solid #000;
      background: yellow;
      text-align:center;
      line-height: 100px;
    }

    #b {
      width:100px;
      height:100px;
      color:white;
      border:1px solid #000;
      background: blue;
      text-align:center;
      line-height: 100px;
      position: fixed;
      top:20px;
      right:10px;
    }

    #c {
      width:100px;
      height:100px;
      color:white;
      border:1px solid #000;
      background: green;
      text-align:center;
      line-height: 100px;
    }
    </style>

  </head>

  <body style="height:2000px;">
    <div id="a">
      aaaaa
    </div>

    <div id="b">
      bbbbb
    </div>

    <div id="c">
      cccccc
    </div>
  </body>
</html>

3-5 index2.html（position:absolute）