HTML/CSS/IE Firefox/opacity
opacity: 0.7
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html>
<head>
<title></title>
<style type="text/css">
div {
padding: 10px;
border: 1px solid black;
opacity: 0.7;
background: #ccc;
}
#div1 {
position: relative;
margin: 50px;
}
#div2 {
position: absolute;
top: 20px;
left: 20px;
}
</style>
</head>
<body>
<div id="div1">
div1
<div id="div2">
div2
</div>
</div>
</body>
</html>