title: apply css class to "button" inside div
body: <p>I have a div containing a button as below,</p>
  
  <pre><code>&lt;div id="parentDiv"&gt;
      &lt;button id="myBtn" class="myclass"&gt;ADD ME&lt;/button&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>a new attribute gets added to this button from JS and it becomes like below ('disabled' attribute is added)</p>
  
  <pre><code>&lt;div id="parentDiv"&gt;
      &lt;button id="myBtn" class="myclass" disabled="disabled"&gt;ADD ME&lt;/button&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>I'm trying to apply below CSS class for disabled button,</p>
  
  <pre><code>#parentDiv button.disabled {
      color: #AAAAAA;
  }
  </code></pre>
  
  <p>But to my surprise this class is not getting applied to button.
  Please point me the correct direction.</p>