not_found.html

<!DOCTYPE html>
<html>
  <head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Page Not Found</title>
    <style>
      body {
        font-family: Arial, Helvetica, sans-serif;
      }
    </style>
  </head>
  <body>
    <center>
      <h1>Page Not Found</h1>
      <h2>The requested web page was not found on this site.</h2>
    </center>
  </body>
</html>