Anida los elementos, me explico table tr td table{
}
Código PHP:
<html>
<head>
<title>probando celdas con link invisible</title>
<style type="text/css">
table{
width:400px;
height:400px;
border:1px solid #000;
}
table tr td{
width:400px;
height:400px;
background-color:#EEEEEE;
}
table tr td table{
background-color:red;
width:200px;
height:200px;
}
table tr td table tr td{
background-color:red;
border:3px dotted #000;
width:200px;
height:200px;
}
</style>
</head>
<body>
<table>
<tr>
<td><table>
<tr>
<td>Interna</td>
</tr>
</table></td>
</tr>
</table>
</body>
</html>