<head>
<style>
#d {
position: relative;
width: 500px;
height: 300px;
background-color: blue;
}
#dcp {
position: relative;
left: 100px;
top: 50px;
width: 300px;
height: 200px;
background-color: red;
clip-path: polygon(3em 0, 100% 0, 100% calc(100% - 3em), calc(100% - 3em) 100% , 0 100%, 0 3em);
}
</style>
</head>
<body>
<div id="d">
<div id="dcp">
clip-path test
<br><br>
clip-path test
</div>
</div>
</body>
