How to add a css class to sidebar first render I am new to drupal theme development . I am customizing a sub theme of zen and wants to change the background of sidebar-first. So I want to know where this sidebar_first render array is defined and how can I add the CSS class to whole sidebar-first also to the nodes within the sidebar_first render array ?

I tried within my templates template.php :

function zensub_page_alter(&amp;$page) {
 $page['sidebar_first'] = array(
 '#attributes' =&gt; array('class' =&gt; 'page-columns')
 );
}


But this causes the sidebar-first remove !
Create a template file with name region--sidebar-first.tpl.php in side the your theme template folder. Copy below code to inside the newly created template file 

&lt;?php if ($content): ?&gt;
     &lt;div class="my_class &lt;?php print $classes; ?&gt;"&gt;
       &lt;?php print $content; ?&gt;
     &lt;/div&gt;
  &lt;?php endif; ?&gt;


replace my_class with you desire class name, clear the drupal cache. It will wrap a new class on the sidebar first region. Good luck