I have a table of data that is generated dynamically based on the contents stored in a mysql database.

This is how my code looks:

<table border="1">
    <tr>
        <th>Name</th>
        <th>Description</th>
        <th>URL</th>
    </tr>
    <?php
        $query = mysql_query("SELECT * FROM categories");
        while ($row = mysql_fetch_assoc($query)) {
            $catName = $row['name'];
            $catDes = $row['description'];
            $catUrl = $row['url'];

            echo "<tr class=''>";
            echo "<td>$catName</td>";
            echo "<td>$catDes</td>";
            echo "<td>$catUrl</td>";
            echo "</tr>";
        }
    ?>
</table>

Now if the table was static, then I would just assign each alternating table row one of 2 styles in repeated order:

.whiteBackground { background-color: #fff; }
.grayBackground { background-color: #ccc; }

and that would be the end of that. However since the table rows are dynamically generated, how can I achieve this?