http://ssrvmbrt.org/css/example.css

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta http-equiv="x-ua-compatible" content="ie=edge">
  <title>404 Error</title>
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <meta name="robots" content="noindex, nofollow">
  <style>
    @media screen and (max-width:500px) {
      body { font-size: .6em; }
    }
  </style>
</head>

<body style="text-align: center;">

  <h1 style="font-family: Georgia, serif; color: #4a4a4a; margin-top: 4em; line-height: 1.5;">
    Sorry, this page doesn't exist.<br>Please check the URL or go back a page.
  </h1>

  <h2 style="  font-family: Verdana, sans-serif; color: #7d7d7d; font-weight: 300;">
    404 Error. Page Not Found.
  </h2>

</body>

</html>