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<!DOCTYPE HTML>
<html><head>
<meta charset="utf-8">
<title></title>
<style type="text/css">
html { padding: 100px }
mask {
position: absolute;
top: 98px; left: 98px;
width: 300px;
height: 200px;
background: black;
}
</style>
</head>
<body>
<mask></mask>
</body>
</html>