くるくるアニメーション その2

    // 右へ進む
    this._frontNo++;
    if (this._frontNo > this._itemCnt) {
       this._frontNo = 1;
    }
    this._pos1stChild++;
    this._parentEle.dataset.front = this._frontNo.toString();
    this._parentEle.style.setProperty('--base-deg', (-360 * this._pos1stChild / this._itemCnt) + 'deg');