html代码：
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title></title>
<style type="text/css">
.out, .in { width: 300px; height: 150px; border: 1px solid #BFBFBF; margin: 20px auto; }
.out { box-shadow: 0px 0px 10px 5px #aaa; }
.in { box-shadow: 0px 0px 10px 5px #aaa inset; }
</style>
</head>
<body>
<div class="out">外部边框阴影</div>
<div class="in">内部边框阴影</div>
</body>
</html>
