Example workflow: NPM scripts to process PostCSS while watching files, starting a server and syncing with the browser.

package.json

{
  "name": "Example",
  "version": "0.0.1",
  "description": "Example workflow",
  "author": "You <you@youremail.com>",
  "license": "MIT",
  "postcss": {
    "plugins": {
      "postcss-easy-import": {},
      "postcss-preset-env": {
        "stage": "0",
        "browsers": "defaults",
        "features": {
          "custom-properties": false
        },
        "preserve": false
      },
      "postcss-clean": {
        "keepSpecialComments": "1"
      }
    }
  },
  "scripts": {
    "css": "postcss assets/postcss/style.css -o assets/css/style.css",
    "watch": "onchange 'assets/postcss/**/*.css' -- npm-run-all css",
    "build": "npm-run-all css",
    "browsersync": "browser-sync start --server --files 'assets/css/style.css'",
    "prestart": "npm-run-all css",
    "start": "npm-run-all --parallel watch browsersync"
  },
  "devDependencies": {
    "browser-sync": "latest",
    "npm-run-all": "latest",
    "onchange": "latest",
    "postcss": "latest",
    "postcss-clean": "latest",
    "postcss-cli": "latest",
    "postcss-easy-import": "latest",
    "postcss-preset-env": "latest"
  }
}