jquery实现固定顶部导航效果(仿蘑菇街)

<p>11111</p>
<p>11111</p>
<p>11111</p>
<p>11111</p>
<p>11111</p>
<p>11111</p>
<p>11111</p>
<p>11111</p>
<p>11111</p>
<p>11111</p>
<p>11111</p>
<p>11111</p>
<p>11111</p>
<p>11111</p>
<p>11111</p>
<p>11111</p>
<p>11111</p>
<p>11111</p>
<p>11111</p>
<p>11111</p>
<p>11111</p>
<p>11111</p>
<p>11111</p>
<p>11111</p>
<p>11111</p>
<p>11111</p>
<p>11111</p>
<p>11111</p>
</div>
</body>
</html>