<!DOCTYPE html>
<html><head><title></title>
<style>
body { margin:0; padding:0; }

#glass {
  opacity:0.4;
  background-color:white;
  position:absolute;
  top:0px; left:0px; right:50px; bottom: 50px;
}
</style>
</head>

<body>
<div id="glass"></div>
</body>
</script>
</html>