<!doctype html>
<html><head>
<title>Border clipping</title>
<style>
.div1 { width: 50px; height: 50px;
border: 10px solid black;
border-radius: 20px;
position: absolute;
background: black;
left: 50px;
top: 50px;
background-clip: padding-box;
}
</style>
</head>
<body>
<div class="div1"></div>
</body></html>