how i header freeze

how i header freeze

demo

how i  header freeze

 <div id="divScroll" style="overflow-x: hidden">
        <table id="tableAppointment" bgcolor="#fcfcfc" border="1" cellspacing="1" width="100%">
           <thead>
                <tr>
                    <td class="csstextheader" width="70px"></td>
                    <td class="csstextheader" width="70px">
                        <b>Time Slot&nbsp;</b>
                    </td>
                    <td><b>Room 7</b></td>
                    <td><b>Room 8</b></td>
                    <td><b>Room 9</b></td>
                    <td><b>Room 10</b></td>
                </tr>
           </thead>
           
          <tbody>
                <tr class="csstablelisttd">
                    <td width="70px">08:00AM</td>
                    <td>00</td>
                    <td class="csstdred">John</td>
                    <td>&nbsp;</td>
                    <td>&nbsp;</td>
                    <td>&nbsp;</td>                                    
                </tr>
</tbody>
        </table>
    </div>