-up':dn_bounce_up}">
        ...
      </div>
    </section>

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

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