注意：本文所有代码基本都为核心代码，如需运行，需添加如下代码段：
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>响应式导航条</title>
<link rel="stylesheet" href="/go.html?url=//maxcdn.bootstrapcdn.com/bootstrap/3.2.0/css/bootstrap.min.css">
<style type="text/css">
body{padding:50px 0 0 0;}
</style>
</head>
<body><!DOCTY
