storeStepScrollOffsets() {
      this.stepScrollOffsets = this.slottedSteps.map(step => {
        const contentItem = this.getStepWrapperByRefId(step._id);
        return contentItem.offsetTop + contentItem.offsetHeight;
      });
    }
Stores the scroll offsets of the steps,
e.g. the steps' starting point.

<b>Note:</b> the disabled ones has negative offsets.
@private