title: how to add class to the wordpress primary dropdown menu
body: <p>I want to add class name to the primary sub-menu in wordpress. Please any one help me to do this. thanks in advance.</p>
  
  <p>for example menu structure like this</p>
  
  <pre><code>&lt;ul id="main-menu"&gt;
  &lt;li&gt;&lt;a href=""&gt; home&lt;/a&gt;&lt;/li&gt;
  &lt;li&gt;&lt;a href=""&gt;About us&lt;/a&gt;
  &lt;ul class="sub-menu"&gt;
  &lt;li&gt;&lt;a href=""&gt;submenu1&lt;/a&gt;&lt;/li&gt;
  &lt;li&gt;&lt;a href=""&gt;submenu2&lt;/a&gt;&lt;/li&gt;
  &lt;li&gt;&lt;a href=""&gt;submenu3&lt;/a&gt;&lt;/li&gt;
  &lt;/ul&gt;
  &lt;/li&gt;
  &lt;/ul&gt;
  </code></pre>
  
  <p>i want to add another class in the sub-menu <code>ul</code></p>