<style>
body {
    z-index: 50;
}
tr:nth-child(even) {
    background-color: #F6F6F7;
}
td {
    width: 150px;
    z-index: 100;
}
th {
    border: 1px solid black;
}
body {
}
.watermark {
    position: absolute;
    color: lightgray;
    opacity: 0.25;
    font-size: 3em;
    width: 50%;
    top: 8%;    
    text-align: center;
    z-index: 0;
}
</style>


<table>
    <div class="watermark">watermark</div>
    <tr>
        <th>1</th>
        <th>2</th>
        <th>3</th>
        <th>4</th>
    </tr>
    <tr>
        <td>asdf</td>
        <td>asdf</td>
        <td>asdfsadf</td>
        <td>asfsadf</td>
    </tr>
    <tr>
        <td>asfs</td>
        <td>asf</td>
        <td>fdew</td>
        <td>asdf</td>
    </tr>
    <tr>
        <td>112</td>
        <td>3435</td>
        <td>1235</td>
        <td>2315</td>
    </tr>
    <tr>
        <td>1235</td>
        <td>987</td>
        <td>458</td>
        <td>159</td>
    </tr>
    <tr>
        <td>asdf</td>
        <td>fdas</td>
        <td>fasdf</td>
        <td>asdf</td>
    </tr>
</table>