The two rows below should look identical.  In both, the spanning cells in columns 2-3 should consume as
much width as possible, while column 1 should be tiny.

<table border=2 height=100% style="-webkit-writing-mode: vertical-rl;">
        <tr>
            <td>1<td colspan=2>2-3
        </tr>
        <tr>
            <td>1</td>
            <td colspan=2 height=100%>2-3</td>
        </tr>
    </table>