public/500.html (13 lines of code) (raw):
<!DOCTYPE html>
<html>
<head>
<title>We're sorry, but something went wrong (500)</title>
<link href="/static.css" media="screen" rel="stylesheet" type="text/css" />
</head>
<body>
<!-- This file lives in public/500.html -->
<div class="dialog">
<h1>500</h1>
<h2>We're sorry, but something went wrong.</h2>
</div>
</body>
</html>