title: change panel heading colour when bootstrap accordion is open
body: <p>When i click on accordion tab its colour has to change indicating the current tab is open. I am using ng2 bootstrap accordion</p>
  
  <pre><code>  &lt;accordion-group #group1 [ngClass]="{'active':group1?.isOpen}" &gt;
   &lt;div accordion-heading &gt; Div 1&lt;/div&gt;
  </code></pre>
  
  <p>and my css</p>
  
  <pre><code>.active[accordion-group] .panel-heading{
    background-color: black;
  }
  </code></pre>
  
  <p>but it didn't work. i referred the angularJS answer mentioned in the post <a href="https://stackoverflow.com/questions/20592441/bootstrap-3-accordion-styling-on-open-closed">Bootstrap 3 accordion styling on open/closed</a>. can someone help me to fix it.</p>