Is it possible to hid sub-categories. I want it to show when visitor click at main categories

Here Are Example My code

<ul>
        <li class="title">Wallpapers</li>
        <li class="group"><a href="#">Car</a></li>
        <li class="group"><a href="#">Animals</a></li>
        <li><a href="#">Cats</a></li>
        <li><a href="#" class="selected">Dogs</a></li>
        <li class="group"><a href="#">Games</a></li>
      </ul>

Thank you for your kind advice

Click events are done with JavaScript, not CSS.