示例：
<!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>
body{
background:#000}
.AlphaBg
{
background:#fff
filter:alpha(opacity=50)
-moz-opacity:0.50
opacity:0.50
width:470px
height:211px
position:
absolute
z-index:30
}
.Contact{
width:470px
height:211px
position:
absolute
z-index:40
color:#fff}
</style>
</head>
<body>
<div
class="AlphaBg"></div>
<div
class="Contact">宽和高与
AlphaBg一样，z-index比
AlphaBg高，position</div>
</body>
</html>
这个是js的<!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/htmlcharset=gb2312" />
<title>Js淡入淡出——Fade效果 - www.codefans.net </title>
<style>
* { font-size:12px}
html { margin:0pxpadding:0pxoverflow:auto}
body { margin:0pxpadding:15pxbackground-color:buttonface}
#w { position:absolutewidth:480pxheight:270pxoverflow:hiddenborder:2px groove #281cursor:default-moz-user-select:nonefilter:alpha(opacity=100)}
#t { line-height:20pxheight:20pxwidth:480pxoverflow:hiddenbackground-color:#27Ccolor:whitefont-weight:boldborder-bottom:1px outset bluetext-align:center}
#winBody { height:248pxwidth:480pxoverflow-x:hiddenoverflow-y:autoborder-top:1px inset bluepadding:10pxtext-indent:10pxbackground-color:white}
</style>
</head>
<body>
<div id="w">
<div id="t">演示Windows的淡入淡出窗口</div>
<div id="winBody">源码爱好者</div>
</div>
</body>
<script>
(function(o,i,s){
i=1s=0.01
setInterval(function(){
i+=ss=i<0?0.01:(i>1?-0.01:s)
if(o.filters)o.filters[0].opacity=i*100
else o.style.opacity=i
},1)
})(document.getElementById("w"))
</script>
</html>
是的，jpg和bmp格式是图像全彩格式，不支持透明的，要做成透明的只能保存成gif格式！ps的具体保存方法是 点 文件->保存为web和设备所用的格式，在那个里面选择gif保存，就可以为透明的了！
