[css] What methods of ‘clearfix’ can I use?

A clearfix is a way for an element to automatically clear after itself, so that you don't need to add additional markup.

.clearfix:after {
   content: " "; /* Older browser do not support empty content */
   visibility: hidden;
   display: block;
   height: 0;
   clear: both;
}
.cleaner {
  clear: both;
}

Normally you would need to do something as follows:

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

With clearfix, you only need to

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