<!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>无标题文档</title>
<style type="text/css">
*{margin:0 auto;}
body{ background:url(sl.jpg) no-repeat; }
.div{background:rgba(0, 0, 0, 0.4) none repeat scroll 0 0 !important;/*实现FF背景透明,文字不透明*/filter:Alpha(opacity=40); background:#000000;/*实现IE背景透明*/color:#FFF;width:500px;height:470px;border:1px
solid #FF0;font-size:18px;text-align:center;font-weight:bold;margin:30px;}
.div p{position:relative;}
</style>
</head>
<body>
<div class="div"><p >我是文字</p></div>
</body>
</html>
IE:外层filter,内层position:relative或absolute。
FF:外层不使用opacity,而用background:rgba()。
<!--
<html>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<head>
<style>
#wrapper
{
background: #369;
width:300px;
height:150px;
}
#div1
{
-moz-opacity: 0.3; /* FF 3.5以下 */
opacity: 0.3; /* FF 3.5及以上 */
filter: alpha(opacity=30); /* IE6及以上 */
background: #fff;
width: 200px;
height: 50px;
}
#div2
{
background: rgba(255, 255, 255, 0.3) !important; /* IE无效,FF有效 */
background: #fff;
filter: alpha(opacity=30);
width: 200px;
height: 50px;
}
#div2 span
{
position: relative;
}
</style>
</head>
<body>
<div id="wrapper">
<div id="div1">
<span>图层背景半透明,字体颜色也半透明</span>
</div>
<br />
<div id="div2">
<span>图层背景半透明,字体颜色不半透明</span>
</div>
</div>
</body>
</html>
-->
.con{
background:rgba(255, 255, 255, 0.8) none repeat scroll 0 0 !important;/*实现FF背景透明,文字不透明*/
filter:Alpha(opacity=80); background:#fff;/*实现IE背景透明*/
}
.con p{ position:relative;}/*实现IE文字不透明*/
<div class="con">
<p>文字</p>
</div>