clearfix fixed hack

.clearfix:after { content: "."; visibility: hidden; display: block; height: 0; clear: both;}

Normally you would need to do something as follows:

<div style="float: left;">Sidebar</div><div style="clear: both;"></div> <!-- Clear the float -->

With clearfix, you only need to

<div style="float: left;" class="clearfix">Sidebar</div><!-- No Clearing div! -->