npm install sass-loader node-sass --save-dev

exports.cssLoaders = function (options) {
 options = options || {}

 var cssLoader = {
  loader: 'css-loader',
  options: {
   minimize: process.env.NODE_ENV === 'production',
   sourceMap: options.sourceMap
  }
 }

 // generate loader string to be used with extract text plugin
 function generateLoaders (loader, loaderOptions) {
  var loaders = [cssLoader]
  if (loader) {
   loaders.push({
    loader: loader + '-loader',
    options: Object.assign({}, loaderOptions, {
     sourceMap: options.sourceMap
    })
   })
  }

  // Extract CSS when that option is specified
  // (which is the case during production build)
  if (options.extract) {
   return ExtractTextPlugin.extract({
    use: loaders,
    fallback: 'vue-style-loader'
   })
  } else {
   return ['vue-style-loader'].concat(loaders)
  }
 }

 // https://vue-loader.vuejs.org/en/configurations/extract-css.html
 return {
  css: generateLoaders(),
  postcss: generateLoaders(),
  less: generateLoaders('less'),
  sass: generateLoaders('sass', { indentedSyntax: true }),
  scss: generateLoaders('sass'),
  stylus: generateLoaders('stylus'),
  styl: generateLoaders('stylus')
 }
}