摘要：<!DOCTYPE html><html><head><meta charset="UTF-8"><title>Document</title><style> li{list-style: none;}
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Document</title>
<style>
li{list-style: none;}
.nav{width: 100px;height: 40px;text-align: center;line-height: 40px;background: #808080;margin-right: 10px;float: left;position: relative;}
.nav:hover .ad{display: block;}
.ad{position: absolute;top: 40px;right: 0px;}
.box{width: 100px;height: 30px;background: #CF7C89;border-bottom: 1px solid black;display: none;}
/* 为什么鼠标移进去nav的盒子会没有效果*/
</style>
</head>
<body>
<ul>
<li>1
<ul>
<li>1</li>
<li>2</li>
<li>3</li>
</ul>
</li>
<li>2
<ul>
<li>1</li>
<li>2</li>
</ul>
</li>
<li>3
<ul>
<li>1</li>
<li>2</li>
<li>3</li>
<li>3</li>
</ul>
</li>
<li>4
<ul>
<li>1</li>
<li>2</li>
<li>3</li>
</ul>
</li>
<li>5
<ul>
<li>1</li>
<li>2</li>
<li>3</li>
<li>2</li>
<li>3</li>
</ul>
</li>
</ul>
</body>
</html>
批改老师：天蓬老师批改时间：2018-10-20 15:40:40
老师总结：代码中没有看到你的class,如果你想让nav下面的盒子显示，要事先隐藏
