title: Add css Class on html element using JavaScript in WordPress
body: <p>I'm working on a theme in WordPress I want to add a new class to an element without removing existing class in this theme there is a place
     to add javascript code in theme option with my new class this button
     will toggle to a form here is the code that I want to add my new
     class into it.</p>
  
  <pre><code>&lt;a href="" target="_self" class="mk-button custom button-5509e751af089 dark-color  flat-dimension large pointed  "&gt;&lt;span&gt;ّFORM&lt;/span&gt;&lt;/a&gt;
  </code></pre>