<!DOCTYPE html>
<html>
<head>
<style>
#myDIV { position: absolute;
width: 300px;
height: 150px;
background-color: lightblue;
border: 1px solid black;
}
#DIV2 { position: relative;
top: 130px;
left: 30px;
width: 300px;
height: 150px;
background-color: coral;
border: 1px solid black;
}
</style>
</head>
<body>
<p>点击“试一试”按钮后，您可看穿蓝色 DIV 元素：</p>
<button onclick="myFunction()">试一试</button>
<div id="DIV2">
<h1>Voila!</h1>
</div>
<div id="myDIV">
</div>
<script>
function myFunction() { document.getElementById("myDIV").style.opacity = "0.5";}
</script>
</body>
</html>