<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8" /><title>无标题文档</title></head><style type="text/css"><!--.news table td{border:1px solid #F00;}.bac table td{border:1px solid #00F;}--></style><body><table width="658" height="317" border="0" cellspacing="0px" class="bac" style="border-collapse:collapse" align="center" id="t1">  <tr>    <td>1</td>    <td>2</td>  </tr>  <tr>    <td colspan="2"><table width="50%" border="0" align="center" class="news" id="t2">      <tr>        <td>3</td>        <td>4</td>        <td>5</td>      </tr>      <tr>        <td> </td>        <td> </td>        <td> </td>      </tr>      <tr>        <td> </td>        <td> </td>        <td> </td>      </tr>    </table></td>  </tr></table></body></html>  楼主,你理解的CSS的优先级有误啊,把你的CSS代码改成如下就可以了:  
  
    <style type="text/css">        table.bac td{            border:1px solid #00f;        }        table.news td{            border:1px solid #F00;        }    </style>     <style type="text/css">        #t1 td{            border:1px solid #00f;        }        #t2 td{            border:1px solid #F00;        }    </style>
                        
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