Remove clearfix from section class in custom theme I'm attempting to edit the template for my pages to allow it to show the content with a block beside it rather than beneath it. I'm currently using bootstrap to lay out my grid. 

In my page.tpl.php I have

&lt;div class="container"&gt;
&lt;div class="col-lg-9"&gt;
    &lt;?php print render($page['content']); ?&gt;
&lt;/div&gt;
&lt;div class="col-lg-3"&gt;
    &lt;?php print render($page['sideblock']); ?&gt;
&lt;/div&gt;
&lt;/div&gt;


I want the content block and the sideblock to be side by side. However when the page renders it wraps the content block in

&lt;section id="block-system-main" class="block block-system clearfix"&gt;


I noticed that when I removed the clearfix class to the section tag I was able to display it side by side. But I don't see any method to remove the clearfix class from this.
For Drupal 8, the best approach for this is to just copy the bootstrap/block/block.html.twig template from the bootstrap theme into your custom themes folder, and just remove the 'clearfix' class from the twig classes block.