Css:背景色透明，内容不透明之终极方法！兼容所有浏览器

没有过多的文字，直接看效果。

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
<title>Css:背景色透明，内容不透明之终极方法！兼容所有浏览器</title>
<style type="text/css">
*{margin:0;padding:0;}
body{background:#3f3f3f;font-family:"宋体", Arial;}
h1, h2, h3, h4, h5, h6{font-weight:normal;font-size:100%;}
img{border:none 0;}
#bos{820px;background:#fff;margin:0 auto;}
#bos ul{zoom:1;overflow:hidden;background:#fff;padding:5px 0 5px 5px;}
#bos ul li{260px;position:relative;overflow:hidden;float:left;margin:5px;background:#fff;}
.img_wrap{258px;border:1px solid #ccc;border-radius:15px;display:block;overflow:hidden;}
#bos ul li h2{100%;height:0px;line-height:50px;color:#fff;text-indent:1em;font-size:14px;font-family:微软雅黑;position:absolute;bottom:0px;border-bottom-left-radius:15px;border-bottom-right-radius:15px;filter:progid:DXImageTransform.Microsoft.gradient(enabled='true',startColorstr='#44000000',endColorstr='#44000000');background:rgba(0,0,0,.6);}
</style>
</head>
<body>
<div id="bos">
<ul>
<li>
<a class="img_wrap" href="#"><img src="http://i2.vanclimg.com/users/18/20120824/n1_120824.jpg" alt="" /></a>
<h2>网站防诈骗重要提示 购物满59元免运费</h2>
</li>
<li>
<a class="img_wrap" href="#"><img src="http://i1.vanclimg.com/users/18/20120824/r1_120824.jpg" alt="" /></a>
<h2>Android客户端升级新体验 配送延误通知</h2>
</li>
<li>
<a class="img_wrap" href="#"><img src="http://i1.vanclimg.com/users/18/20120824/f8_120824.jpg" alt="" /></a>
<h2>陈年谈品牌的本分 工行e支付可直减60元</h2>
</li>
<li>
<a class="img_wrap" href="#"><img src="http://i2.vanclimg.com/users/18/20120824/n1_120824.jpg" alt="" /></a>
<h2>陈年谈品牌的本分 工行e支付可直减60元</h2>
</li>
<li>
<a class="img_wrap" href="#"><img src="http://i1.vanclimg.com/users/18/20120824/f8_120824.jpg" alt="" /></a>
<h2>陈年谈品牌的本分 工行e支付可直减60元</h2>
</li>
<li>
<a class="img_wrap" href="#"><img src="http://i2.vanclimg.com/users/18/20120824/n1_120824.jpg" alt="" /></a>
<h2>陈年谈品牌的本分 工行e支付可直减60元</h2>
</li>
</ul>
</div>
  <script type="text/javascript">
     var bos = document.getElementById('bos');
     var lis = bos.getElementsByTagName('li');
     var len = lis.length;
     while (len--) {
         lis[len].onmouseover = function () {
             over(this.getElementsByTagName('h2')[0]);
         }
         lis[len].onmouseout = function () {
             out(this.getElementsByTagName('h2')[0]);
         }
     }
     function over(obj) {
         var ypos = 0;
         if (obj.time) {
             clearInterval(obj.time)
         }
         obj.time = setInterval(function () {
             if (ypos < 50) {
                 ypos += Math.ceil((50 - ypos) / 3);
             }
             obj.style.height = ypos + "px";
         }, 25);
     }
     function out(obj) {
         var ypos = 50;
         if (obj.time) {
             clearInterval(obj.time)
         }
         obj.time = setInterval(function () {
             if (ypos >= 0) {
                 ypos -= Math.ceil((ypos - 0) / 3);
             }
             obj.style.height = ypos + "px";
         }, 25);
     }
     // js代码解释权归华仔所有
</script></body>
</html>