Column borders to fill the entire table even if not enough data

Im making a dynamic table and i dont know how many trs i will have:

<!-- language: lang-html-->
<div style="height: 20cm">
<table cellpadding="0" cellspacing="0" style="border-spacing:0;border-collapse:0;font-size:12px;width: 100%;text-transform:uppercase;">
    <thead>
        <tr style="font-weight:bold">
            <th style="width:9%;border-bottom:1px solid black;padding:6px;" align="center">cantidad</th>
            <th style="width:12%;border:1px solid black;border-top:0 none;padding:6px;" align="center">codigo</th>
            <th style="width:79%;border-bottom:1px solid black;padding:6px;align: center" align="center">descripcion</th>
        </tr>
    </thead>
    <tbody style="border-bottom: none;">    
        <tr t-foreach="o.pack_operation_ids" t-as="l">
            <td style="border-bottom:0 none;border-right: 1px solid black;border-top: 0 none;padding: 0px 0px 0px 5px"><span t-field="l.product_qty"/></td>
            <td style="border-right:1px solid black;border-top:0 none; padding: 0px 0px 0px 5px"><span t-field="l.product_id.default_code"/></td>
            <td style="border-bottom:0 none; border-top: 0 none; padding: 0px 0px 0px 5px"><span t-field="l.product_id.name"/>           <span t-field="l.lot_id.name"/>  <span t-field="l.lot_id.life_date" t-field-options='{"format": "dd/MM/yyyy"}'/></td>
        </tr>
    </tbody>    
</table>

Thing is that i need the borders to fill the entire div (to the bottom line), i dont care about the amounts of rows that i will have.

Hope some one can help, thanks in advance.