<div runat="server" id='MainDiv' style='overflow:auto;top:40px;left:10px;' class='coolScrollBar'>
<table runat="server"  border='1'  id ="MainTable" style="font-size:9pt;table-layout:fixed" bordercolor='#000000' cellpadding='2' cellspacing='0'  borderColorDark='#ffffff'  borderColorLight='#003042' onkeydown="InputGrid_SetKeyDown()">
 <tr class="">
    <td style="width:31px" align="center" >序号</td>
 </tr>
</table>
</div>请问这个第一行怎么做到表头固定