Crear Excel de forma básica

header('Content-Type: text/html; charset=iso-8859-1');
session_start();
require_once ('librerias/cnn_bd.php');
$db = new db;
$sql = "select * from ...";
$regAux = mysqli_query($db->cnn, $sql);

header('Pragma: ');
header('Cache-Control: ');
header('Content-Type: application/vnd.ms-excel');
header('Content-Disposition: attachment; filename=excel_lsg.xls');
?>
<style type="text/css">
    * {
        font-family: Verdana, Arial, Helvetica, sans-serif;
        font-size: 10px;
    }
    table {border-collapse: collapse;}
    .datos {border: 1px solid #000000}
    .cabecera {
        background-color: #F9D119;
        color: #000000;
        text-align: left;
        font-weight:bold;
    }
</style>

<table cellpadding="3" cellspacing="0" class="datos" border="1">
    <tr>
        <th class="cabecera">xxx</th>
        <th class="cabecera">xxx</th>
        <th class="cabecera">xxx</th>
    </tr>
    <?php
    while ($rowAux = $regAux->fetch_assoc()) {  ?>
        <tr>
            <td class="datos"> <?=$rowPS["..."];?></td>
            <td class="datos"> <?=$rowPS["..."];?> </td>
            <td class="datos"> <?=$rowPS[".."];?> </td>
        </tr>
        <?php
    }
    ?>
</table>