<!DOCTYPE html>
<html>
<head>
<style type="text/css" media="screen">
.wrapper {
outline: 1px solid black;
width: 280px;
height: 280px;
-webkit-box-sizing: border-box;
margin: 4px;
display: inline-block;
}
.box {
position: relative;
width: 280px;
height: 280px;
display: inline-block;
}
.indicator {
position: absolute;
width: 280px;
height: 280px;
-webkit-box-sizing: border-box;
border: 0 solid rgba(0, 255, 0, 0.05);
}
</style>
</head>
<body>
<!-- The extent of the shadow should approximately match the pale green boxes. -->
<div class="wrapper">
<div class="indicator box" style="border-width: 10px"></div>
<div class="box" style="box-shadow: 0 0 10px black inset"></div>
</div>
<div class="wrapper">
<div class="indicator box" style="border-width: 20px"></div>
<div class="box" style="box-shadow: 0 0 20px black inset"></div>
</div>
<br>
<div class="wrapper">
<div class="indicator box" style="border-width: 50px"></div>
<div class="box" style="box-shadow: 0 0 50px black inset"></div>
</div>
<div class="wrapper">
<div class="indicator box" style="border-width: 90px"></div>
<div class="box" style="box-shadow: 0 0 90px black inset"></div>
</div>
</body>
</html>