请教下我的背景图片定位后效果出不来？
代码：
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title></title>
<style type="text/css">
*{margin: 0;padding: 0;}
ul{list-style-type: none;}
h3{font-size: 14px;
font-weight: 400;
}
li{display: block;
height: 31px;
line-height: 31px;
overflow: hidden;
border-bottom: 1px solid #dedede;
margin: 3px 10px 0 0;
}
.cat{width: 150px;
background: #f8f8f8;
border: 1px solid #ddd;
}
i{background: url(img/sidebar.png);
display:inline;
width: 34px;
height: 24px;
float: left;}
.cat-1 i{background-position: 0 0;}
.cat-2 i{background-position: 0 -24px;}
.cat-3 i{background-position: 0 -48px;}
.cat-4 i{background-position: 0 -72px;}
.cat-5 i{background-position: 0 -96px;}
.cat-6 i{background-position: 0 -120px;}
.cat-7 i{background-position: 0 -144px;}
.cat-8 i{background-position: 0 -168px;}
</style>
</head>
<body>
<div class="cat">
<ul>
<li class="=cat-1">
<i></i>
<h3>服装内衣</h3>
</li>
<li class="=cat-2">
<i></i>
<h3>鞋包配饰</h3>
</li>
<li class="=cat-3">
<i></i>
<h3>户外运动</h3>
</li>
<li class="=cat-4">
<i></i>
<h3>珠宝手表</h3>
</li>
<li class="=cat-5">
<i></i>
<h3>手机数码</h3>
</li>
<li class="=cat-6">
<i></i>
<h3>办公电脑</h3>
</li>
<li class="=cat-7">
<i></i>
<h3>护肤彩妆</h3>
</li>
<li class="=cat-8">
<i></i>
<h3>母婴用品</h3>
</li>
</ul>
</div>
</body>
</html>
