防止select遮挡
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<title>Untitled Document</title>
</head>
<body>
<div style="position:absolute;background:red;width:100px;height:200px;z-index:10000;left:20px;top:20px;">
<iframe style="position:absolute;width:100%;height:100%;_filter:alpha(opacity=0);opacity=0;border-style:none;"></iframe>
</div>
<select><option>sdf</option></select>
dfgdfgdfgdfgdfgdfgdfgdfgdfdfgdfgdfgdfgdfgdfgdfgdfgddfgdfgdfgdfgdfgdfgdfgdfgd
dfgdfgdfgdfgdfgdfgdfgdfgdf
</body>
</html>
