margin属性可任意拆分为左，右页边距设置自动指定，结果都是出现居中元素 - 在线编辑器

          <!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <style>
    .center {
      margin: auto;
      width: 70%;
      background-color: #b0e0e6;
    }
  </style>
</head>

<body>
  <div class="center">
    <p>In my younger and more vulnerable years my father gave me some advice that I've been turning over in my mind ever since.</p>
    <p>'Whenever you feel like criticizing anyone,' he told me, 'just remember that all the people in this world haven't had the advantages that you've had.'</p>
  </div>
  <p><b>注意: </b>使用 margin:auto 无法兼容 IE8, 除非 !DOCTYPE 已经声明.</p>
</body>
</html>
        