404.html

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="utf-8">
    <meta http-equiv="x-ua-compatible" content="ie=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <link href="assets/css/style.css" rel="stylesheet">
    <title>Redirecting </title>
</head>

<body onload="redirect()">
    <header>
        <div class="logo">
            <h1><a href="index.html">The Overlay Test</a></h1>
        </div>
    </header>
    <h2 class="headings">Redirecting....</h2>
    <h3 class="sub-headings">Back to The Overlay Test</h3>
    <script>
        function redirect() {
            setTimeout(function () {
                window.location.replace("index.html");
            }, 600);
        }
    </script>
</body>

</html>