async _showAnimation({ contentNode }) {
    const expectedHeight = await this.__calculateHeight(contentNode);
    contentNode.style.setProperty('opacity', '1');
    contentNode.style.setProperty('padding', '12px 0');
    contentNode.style.setProperty('max-height', '0px');
    // @ts-ignore
    // eslint-disable-next-line no-promise-executor-return
    await new Promise(resolve => requestAnimationFrame(() => resolve()));
    contentNode.style.setProperty('max-height', expectedHeight);
    await this._waitForTransition({ contentNode });
  }
Trigger show animation and wait for transition to be finished.
@param {Object} options - element node and its options
@param {HTMLElement} options.contentNode
@override