출처: https://worker-k.tistory.com/entry/css-%EC%84%A0%ED%83%9D%EC%9E%90-nth-child-%EB%B0%8F-nth-of-type-%EA%B4%84%ED%98%B8%EC%97%90-%ED%94%8C%EB%9F%AC%EC%8A%A4-%EB%A7%88%EC%9D%B4%EB%84%88%EC%8A%A4-%EA%B3%B1%ED%95%98%EA%B8%B0-%EC%88%98%EC%8B%9D%EC%82%AC%EC%9A%A9
