Use <div class="three column">
within it’s parent <div class="section">
element add up to 6.
<div class="six_column section">
<div class="two column">
<div class="column_content">
...
</div>
</div>
<div class="three column">
<div class="column_content">
...
</div>
</div>
<div class="one column">
<div class="column_content">
...
</div>
</div>
</div>