not-found.html

<!DOCTYPE html>
<html>

<head>
    <meta charset="UTF-8">
    <title>Sign Up</title>
    <link rel="stylesheet" href="./css/bootstrap.min.css">
    <link rel="stylesheet" href="./fontawesome-free-5.13.0-web/css/all.css">
    <style>
        body, html {
            height: 100%;
        }
        .activeErr
        {
            padding: 0.5rem;
            border: 1px solid red;
        }
    </style>
</head>

<body>
    <div class="d-flex" style="height: 90%;">
        <div class="row m-auto w-100">
            <div class="mx-auto" style="width: 350px;">
                <div class="card bg-light text-dark">
                    <article  style = "font-size: 2.5em;text-align: center;">
                      404 Not found
                    </article>
                </div>
            </div>
        </div>
    </div>
</body>
<script src="client/header.js"></script>
</html>