<style>
table {
width: 100%;
}
td {
border: 1px solid #777;
padding: 10px;
}
td:first-child {
width: 30%;
}
</style>
<table>
<tr>
<td>a</td>
<td colspan="3">b</td>
<td colspan="3">c</td>
</tr>
<tr>
<td>a</td>
<td colspan="2">b</td>
<td colspan="2">c</td>
<td colspan="2">d</td>
</tr>
</table>