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>
<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>
<head>
<style>
.t1{background-color:red}
.t2 td{background-color:blue}
</style>
</head>
<table border="1" width="100" class=t1>
<tr>
<td width="100%"> </td>
</tr>
</table>
<table border="1" width="100" class=t2>
<tr>
<td width="100%"> </td>
</tr>
</table>