 function() {
      this.classList.add('no-padding');
      this._ensureTarget();
      requestAnimationFrame(this._scroll.bind(this));
    },

    _scroll: function() {
      this.toggleClass('is-scrolled', this.scrollTarget.scrollTop > 0);
      this.toggleClass('can-scroll', this.scrollTarget.offsetHeight < this.scrollTarget.scrollHeight);
      this.toggleClass('scrolled-to-bottom',
        this.scrollTarget.scrollTop + this.scrollTarget.offsetHeight >= this.scrollTarget.scrollHeight);
    },

    _ensu