css variables & CSS 变量
https://gist.github.com/xgqfrms-GitHub/5d022a13292c615d2730e84d909e1aba
css-variables
https://developer.mozilla.org/zh-CN/docs/Web/CSS/Using_CSS_variables
https://css-tricks.com/difference-between-types-of-css-variables/
http://www.ruanyifeng.com/blog/2017/05/css-variables.html
css-variables
http://www.ruanyifeng.com/blog/2017/05/css-variables.html
https://css-tricks.com/making-custom-properties-css-variables-dynamic/
https://scotch.io/tutorials/improve-the-performance-of-your-javascript-web-application
https://danielcwilson.com/blog/2017/02/individual-transforms/