setItemTransitions(items) {
    const { speed, easing } = this.options;
    const positionProps = this.options.useTransforms ? ['transform'] : ['top', 'left'];

    // Allow users to transition other properties if they exist in the `before`
    // css mapping of the shuffle item.
    const cssProps = Object.keys(ShuffleItem.Css.HIDDEN.before).map((k) => hyphenate(k));
    const properties = positionProps.concat(cssProps).join();

    items.forEach((item) => {
      item.element.style.transitionDuration = `${speed}ms`;
      item.element.style.transitionTimingFunction = easing;
      item.element.style.transitionProperty = properties;
    });
  }
Sets css transform transition on a group of elements. This is not executed
at the same time as `item.init` so that transitions don't occur upon
initialization of a new Shuffle instance.
@param {ShuffleItem[]} items Shuffle items to set transitions on.
@protected