gulp-postcss + autoprefixer

gulpfile.js

var gulp        = require('gulp'),
    postcss     = require('gulp-postcss'),
    autoprefix  = require('autoprefixer-core');

gulp.task('css', function() {
  return gulp.src('test.css')
    .pipe(postcss([ autoprefix() ]))
    .pipe(gulp.dest('dist/css'));
});

gulp.task('default', [ 'css' ]);

package.json

{
  "scripts": {
    "start": "gulp"
  },

  "devDependencies": {
    "autoprefixer-core": "^5.1.8",
    "gulp": "^3.8.11",
    "gulp-postcss": "^5.1.0",
  }
}

test.css

.container {
  display: flex;
}

run with npm start