<style type="text/css">
ul,li{ padding:0; margin:0; overflow:hidden;}
li{ list-style:none;}
img{ border:0;}
.box{ width:950px;}
.box li{ float:left; width:300px; height:250px; margin-right:10px; margin-bottom:20px;}
#box_img1 {width: 300px;
height: 250px;background-image: url('support.png');}
#box_img1 a:hover {width: 300px;
height: 250px;background-image:url('GotJobButton.png');}
#box_img2 {width: 300px;
height: 250px;background-image: url('support.png');}
#box_img2 a:hover {width: 300px;
height: 250px;background-image:url('object.png');}
</style>
<ul class="box">
<li id="box_img1"><a href="features/businesses"></a></li>
<li id="box_img2"><a href="features/nonprofits"></a></li>
</ul>
问题:我想让它在鼠标悬停时改变图片。但它不起作用,那么这里出了什么问题?