index.html代码内容
<!DOCTYPE html>
<html>
<head>
<meta charset=utf-8>
<title>导航高亮显示</title>
<style type=text/css>
body{
font-size:20px;
}
.nav{
list-style-type: none;
margin:0;
padding:0;
}
.clear:after{
content:'/20';
display:block;
clear:both;
height:0;
visi
