<!DOCTYPE html>
<html>
<style>
tr.top td {
border-top: thin solid black;
}
tr.bottom td {
border-bottom: thin solid black;
}
tr.row td:first-child {
border-left: thin solid black;
}
tr.row td:last-child {
border-right: thin solid black;
}
</style>
<html>
<head>
</head>
<body>
<table cellspacing="0">
<tr>
<td>no border</td>
<td>no border here either</td>
</tr>
<tr class="top row">
<td>one</td>
<td>two</td>
</tr>
<tr class="bottom row">
<td>three</td>
<td>four</td>
</tr>
<tr>
<td colspan="2">once again no borders</td>
</tr>
<tr class="top bottom row">
<td colspan="2">hello</td>
</tr>
<tr>
<td colspan="2">world</td>
</tr>
</table>
</body>