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

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

    <section>
      <h2>.dn-rota