横向滚动条表头跟着动，纵向滚动条，表头不动，求大神帮忙解答下。。
<div id = "selectday" style="position:absolute; height:542px; width:500px;overflow-x:auto "> 
 <table id="tb0" width=800px;>
  <tr>
   <td width="80">a0</td>
   <td width="80">a1</td>
   <td width="80">a2</td>
   <td width="80">a3</td>
   <td width="80">a4</td>
   <td width="80">a5</td>
   <td width="80">a6</td>
   <td width="80">a7</td>
   <td width="80">a8</td>
   <td width="80">a9</td>
  </tr>
 </table>
<table id="tb1" width=800px;>
  <tr>
   <td width="80">00</td>
   <td width="80">11</td>
   <td width="80">22</td>
   <td width="80">33</td>
   <td width="80">44</td>
   <td width="80">55</td>
   <td width="80">66</td>
   <td width="80">77</td>
   <td width="80">88</td>
   <td width="80">99</td>
  </tr>
  <tr>
   <td width="80">00</td>
   <td width="80">11</td>
   <td width="80">22</td>
   <td width="80">33</td>
   <td width="80">44</td>
   <td width="80">55</td>
   <td width="80">66</td>
   <td width="80">77</td>
   <td width="80">88</td>
   <td width="80">99</td>
  </tr>
  <tr>
   <td width="80">00</td>
   <td width="80">11</td>
   <td width="80">22</td>
   <td width="80">33</td>
   <td width="80">44</td>
   <td width="80">55</td>
   <td width="80">66</td>
   <td width="80">77</td>
   <td width="80">88</td>
   <td width="80">99</td>