Don't gossip, just go to the code!
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title></title><style type="text/css">
.div1{
position: absolute;
top: 200px;
min-height: 100px;
width: 400px;
border: 1px solid ;
}
.div1::after{
content: "";
border: 30px solid transparent;
border-left-color: white;
position: absolute;
top: 10px;
left: 399px;
}
.div1::before{
content: "";
border: 30px solid transparent;
border-left-color: black;
position: absolute;
top:10px;
left: 400px;
}
</style>
</head>
<body>
<div class="div1">
</div>
</body>
</html>
The effect is as follows
