<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title></title>
<style type="text/css">
*{
margin: 0;
padding: 0;
}
ul{
position: absolute;
left: 100px;
width: 500px;
height: 100px;
background-color: #A0522D;
}
li{
box-sizing: border-box;
float: left;
width: 50px;
height: 100px;
background-color: #0070C9;
border: 1px white solid;
list-style: none;
position: relative;
}
.aa{
width: 300px;
}
.last{
position: absolute;
right: 0;
top: 0;
}
</style>
</head>
<body>
<ul id="box">
<li class="aa">1</li>
<li class="">2</li>
<li class="">3</li>
<li class="">4</li>
<li class="last">5</li>
</ul>
<script src="../jQuery/jquery.js" type="text/javascript" charset="utf-8"></script>
<script type="text/javascript">
$(function(){
$(‘#box li‘).mouseover(function(){
//让指定li变宽 让其他li变窄
$(this).stop().animate({‘width‘:‘300px‘},800).find().end().siblings().stop().animate({‘width‘:‘50px‘},800)
})
})
</script>
</body>
</html>
原文：https://blog.51cto.com/13571682/2474142