<!DOCTYPE html>
<p>There should be a green square below.</p>
<div style="columns:1;">
<div style="float:left; width:40px; height:40px; background:green;"></div>
<div style="column-span:all;"></div>
</div>
<!DOCTYPE html>
<p>There should be a green square below.</p>
<div style="columns:1;">
<div style="float:left; width:40px; height:40px; background:green;"></div>
<div style="column-span:all;"></div>
</div>