我想做两张图片重叠 上边的图片透明 该如何做呢 初学者 求指教！！
html
css
图片
------解决方案--------------------
<!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">
#logo{background:url(https://developer.cdn.mozilla.net/media/img/mdn-logo-sm.png)no-repeat center;width:62px;height:71px;}
#logo img{filter:alpha(opacity=50); -moz-opacity:0.5; opacity:0.5;}
</style>
</head>
<body>
<div id="logo">
<img src="https://mozorg.cdn.mozilla.net/media/img/firefox/new/header-firefox.png?2013-06" />
</div>
</body>
</html>