부드러운 전환을 가능하게 해준다.
https://www.w3schools.com/cssref/pr_class_position.asp
https://codepen.io/rstacruz/pen/oxJqNv
https://codepen.io/daleseo/pen/QWpOyoG
ref : https://codepen.io/Shesam1/pen/qYWewx
ref: https://studiomeal.com/archives/197
모질라 : https://developer.mozilla.org/ko/docs/Learn/CSS/CSS_layout/Media_queries
1 그리드 기본: https://goddino.tistory.com/246