test:/\.css$/,
use: ['style-loader','css-loader',{
  loader: "postcss-loader",
  options:{
    plugins:[
      require("autoprefixer")({
        browsers: [
          'ie >= 8',
          'Firefox >= 20',
          'Safari >= 5',
          'Android >= 4',
          'Ios >= 6',
          'last 4 version'
        ]
      })
    ]
  }
}]

const postcssLoader = {
  loader: 'postcss-loader',
  options: {
   sourceMap: options.sourceMap
  }
}

function generateLoaders (loader, loaderOptions) {
  const loaders = [cssLoader]
  if (loader) {
   loaders.push({
    loader: loader + '-loader',
    options: Object.assign({}, loaderOptions, {
     sourceMap: options.sourceMap
    })
   })
  }
  loaders.push(postcssLoader)
  ......
}

// https://github.com/michael-ciniawsky/postcss-load-config

module.exports = {
 "plugins": {
  "postcss-import": {},
  "postcss-url": {},
  // to edit target browsers: use "browserslist" field in package.json
  "autoprefixer": {}
 }
}

"browserslist": [
  "last 10 Chrome versions",
  "last 5 Firefox versions",
  "Safari >= 6",
  "ie > 8"
 ]

npm install postcss-import --save-dev
npm install postcss-loader --save-dev
npm install postcss-url --save-dev
npm install autoprefixer --save-dev