getClosestStepIndexByScrollPos(scrollPos) {
      for (let closestStepIndex = 0; closestStepIndex <= this.stepScrollOffsets.length - 1; closestStepIndex++) {
        const stepScrollOffset = this.stepScrollOffsets[closestStepIndex];
        const step = this.getStepWrapperByIdx(closestStepIndex);
        const switchStepBoundary = step.offsetTop + step.offsetHeight * this.effectiveStepSwitchThreshold;
        if (stepScrollOffset > 0 && scrollPos < stepScrollOffset) {
          if (scrollPos > switchStepBoundary) {
            return closestStepIndex + 1;
          }
          return closestStepIndex;
        }
      }
      return this.selectedStepIndex;
    }
Returns the closest step index by given scroll position.
@private
@param {Integer} scrollPos the scroll position