html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>Document</title>
</head>
<body>
<div class="rectangle">
</div>
</body>
<style>
.rectangle {
height: 0;
width: 0;
border-left: 50px solid transparent;
border-right: 50px solid transparent;
border-top: 0;
border-bottom: 50px solid #f40355;
}
</style>
</html>