需要注意的是 hover中要给盒子加:position:relative;
<style type="text/css">
*{margin:0;padding:0;}
.boxin{150px;height:300px;border:1px solid #ccc;float: left;margin-left:-1px;}
.boxin:hover{border:1px solid #f40; position: relative;}
</style>
</head>
<body>
<div id="box">
<div class="boxin"></div>
<div class="boxin"></div>
<div class="boxin"></div>
<div class="boxin"></div>
<div class="boxin"></div>
<div class="boxin"></div>
</div>
</body>
提醒：如果.boxin的父类是个定位，那么需要设置.boxin:hover的层级--------z-index:1(设置当前的层级比其他要高)