1. 安装:

yarn add sass-loader@7.3.1 --dev
yarn add node-sass --dev

注:
①. sass-loader依赖于node-sass

(1). 报错:

Module build failed: TypeError: this.getResolve is not a function
at Object.loader (path/node_modules/sass-loader/dist/index.js:52:26)

2. 注释:

①. /* */         => css中显示
②. //            => css中不显示
③. /*重要注释!*/   => 压缩不会被删掉