 z-index only at the end of the animation.
      this.style.zIndex = '';
      this.notifyResize();
      this.__isAnimating = false;
      this.fire('iron-overlay-closed', this.closingReason);
    },

    _preparePositioning: function() {
      this.style.transition = this.style.webkitTransition = 'none';
      this.style.transform = this.style.webkitTransform = 'none';
      this.style.display = '';
    },

    _finishPositioning: function() {
      // First, make it invisible & reactivate animations.
   