<!DOCTYPE html>

<html>
    <head>
        <script src="https://code.jquery.com/jquery-3.1.0.min.js"></script>
        <script>

            $(function() {
                $('.door').click(function() {
                    $(this).removeClass('closed');
                });
            });

        </script>
        <style>

            body {
                background-color: #000;
            }

            .closed {
                background-color: #fff;
            }

            .door {
                color: #fff;
                font-family: sans-serif;
                font-size: 60px;
                font-weight: bold;
                height: 150px;
                padding-top: 50px;
                margin: 20px;
                text-align: center;
                width : 100px;
            }

        </style>
        <title>doors-0</title>
    </head>
    <body>
        <table>
            <tr>
                <td><div class="closed door">15</div></td>
                <td><div class="closed door">23</div></td>
                <td><div class="closed door">16</div></td>
                <td><div class="closed door">8</div></td>
                <td><div class="closed door">42</div></td>
                <td><div class="closed door">50</div></td>
                <td><div class="closed door">4</div></td>
            </tr>
        </table>
    </body>
</html>