_flip_y">Toggle Class</button>
      <div class="element" ng-class="{'dn-flip-y':dn_flip_y}">
        ...
      </div>
    </section>

    <section>
      <h2>.dn-bounce</h2>
      <button ng-click="dn_bounce=!dn_bounce">Toggle Class</button>
      <div class="element" ng-class="{'dn-bounce':dn_bounce}">
        ...
      </div>
    </section>

    <section>
      <h2>.dn-bounce-up</h2>
      <button ng-click="dn_bounce_up=!dn_bounce_up">Toggle Class</button>
      <div class="element" ng-class="{'dn-bounce