html,css 참고자료

em

https://www.daleseo.com/css-em-rem/

flex

https://studiomeal.com/archives/197

grid

https://studiomeal.com/archives/533

defer

http://www.tcpschool.com/html-tag-attrs/script-defer

가운데 정렬

https://brunch.co.kr/@skykamja24/514