refer to

How to Setup npm and scss \ sass

npm install node-sass --save-dev
mkdir -p src/styles
touch src/styles/styles.scss

In your generated package.json add the following to your scripts entry

"scripts": {
  "compile:sass": "node-sass src/styles -o dist/styles --source-comments=false --source-map=true --output-style=compressed --error-bell",
  "watch:sass": "npm run compile:sass -- --watch",  
  "watch": "npm run watch:sass"

Then to get up and running, just do the following in your command line \ terminal

npm run compile:sass
npm run watch:sass

If you wish to compile just one file

"scripts": {
  "compile:sass": "node-sass input-file.css output-file.css"