利用CSS代码让Table产生固定表头

<style type="text/css">  <!--  body,table, td, a {font:9pt;}  /*重点：固定行头样式*/  .scrollRowThead{position: relative; left: expression(this.parentElement.parentElement.parentElement.parentElement.scrollLeft);z-index:0;}  /*重点：固定表头样式*/  .scrollColThead {position: relative;top: expression(this.parentElement.parentElement.parentElement.scrollTop);z-index:2;}  /*行列交叉的地方*/  .scrollCR { z-index:3;}  /*div外框*/  .scrollDiv {height:200px;clear: both; border: 1px solid #EEEEEE;OVERFLOW: scroll;width: 320px; }  /*行头居中*/  .scrollColThead td,.scrollColThead th{ text-align: center ;}  /*行头列头背景*/  .scrollRowThead,.scrollColThead td,.scrollColThead th{background-color:EEEEEE;}  /*表格的线*/  .scrolltable{border-bottom:1px solid #CCCCCC; border-right:1px solid #CCCCCC; }  /*单元格的线等*/  .scrolltable td,.scrollTable th{border-left: 1px solid #CCCCCC; border-top: 1px solid #CCCCCC; padding: 5px; }    .scrollTable thead th{background-color:#EEEEEE;font-weight:bold;position:relative;}  -->  </style>    <h1>利用CSS代码让Table产生固定表头</h1>  <div id="scrollDiv" >  <table border="0" cellpadding="3" cellspacing="0" width="500"  >    <th  > </th>    <th colspan="2">列头</th>    <th colspan="2">列头</th>    <th rowspan="2">列头</th>  </tr>  <tr  >    <th  >h1</th>    <th >h2</th>    <th >h3</th>    <th >h4</th>    <th >h5</th>  </tr>  </thead>  <tr>    <td  >      <input type="checkbox" name="checkbox" value="checkbox">      a</td>    <td>单元格2</td>    <td>单元格3</td>    <td>单元格4</td>    <td>单元格5</td>    <td>单元格5</td>  </tr>  <tr>    <td  >      <input type="checkbox" name="checkbox2" value="checkbox">      b</td>    <td>单元格2</td>    <td>单元格3</td>    <td>单元格4</td>    <td>单元格5</td>    <td>单元格5</td>  </tr>  <tr>    <td nowrap  >      <input type="checkbox" name="checkbox3" value="checkbox">      c</td>    <td nowrap>单元格2</td>    <td nowrap>单元格3</td>    <td nowrap>单元格4</td>    <td nowrap>单元格5</td>    <td nowrap>单元格5</td>  </tr>  <tr>    <td  >      <input type="checkbox" name="checkbox4" value="checkbox">      d</td>    <td>单元格2</td>    <td>单元格3</td>    <td>单元格4</td>    <td>单元格5</td>    <td>单元格5</td>  </tr>  <tr>    <td  >      <input type="checkbox" name="checkbox5" value="checkbox">      e</td>    <td>单元格2</td>    <td>单元格3</td>    <td>单元格4</td>    <td>单元格5</td>    <td>单元格5</td>  </tr>  <tr>    <td  >      <input type="checkbox" name="checkbox6" value="checkbox">      f</td>    <td>单元格2</td>    <td>单元格3</td>    <td>单元格4</td>    <td>单元格5</td>    <td>单元格5</td>  </tr>  <tr>    <td >      <input type="checkbox" name="checkbox7" value="checkbox">      g</td>    <td>单元格2</td>    <td>单元格3</td>    <td>单元格4</td>    <td>单元格5</td>    <td>单元格5</td>  </tr>  </table>  </div>