<!DOCTYPE html>
<html lang="en">
<head>
<style>
div {
    width: 220px;
    height: 220px;
    background-color: green;
    -webkit-clip-path: polygon(0 0, 200px 0, 200px 200px, 0 200px, 0 20px, 180px 20px, 180px 180px, 20px 180px, 20px 20px, 0 20px);
}
</style>
</head>
<body>
<div>
</body>
</html>