try it like this
<head>
<style>
#t1 td{background-color:red}
#t2 td{background-color:blue}
</style>
</head>
<table border="1" width="100" id=t1>
  <tr>
    <td width="100%"> </td>
  </tr>
</table>
<table border="1" width="100" id=t2>
  <tr>
    <td width="100%"> </td>
  </tr>
</table>