JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8" />
<title>Untitled Document</title>
</head>
<body>
<div style="border:1px solid #000; height:400px; width:400px; margin:50px auto; position:relative;">
    <span class="arrow"></span>
</div>
</body>
</html>

CSS

.arrow {
     border:50px outset transparent ;
     border-top:#eee 50px solid;
     display:block;
     height:0;
     width:0;
     top:50%;
     right:50%;
     position:absolute;
}