title: How to add a css class to this php code
body: <p>I am wondering how to add a css class to this part of the code which is linking to the older posts on a blog.</p>
  
  <pre><code>&lt;?php posts_nav_link(' — ', __('« go back'), __('keep looking »')); ?&gt;
  </code></pre>
  
  <p>Thanks!</p>