Add an attribute colspan
(abbriviation for 'column span') in your top cell (<td>
) and set its value to 2.
Your table should resembles the following;
<table>
<tr>
<td colspan = "2">
<!-- Merged Columns -->
</td>
</tr>
<tr>
<td>
<!-- Column 1 -->
</td>
<td>
<!-- Column 2 -->
</td>
</tr>
</table>
See also
W3 official docs on HTML Tables