css 九宫格

 

http://jsfiddle.net/webtiki/kQXkt/

 

http://jsfiddle.net/webtiki/MpXYr/3/embedded/

 

https://www.web-tinker.com/article/20778.html

 

https://idiotwu.me/study/responsive-square/#viewwidth

 

https://idiotwu.me/css-responsive-square/