Compiling SUIT with gulp and postcss

example.js

var gulp = require('gulp');
var bemLinter = require('postcss-bem-linter');
var atImport = require('postcss-import');
var cssnext = require('cssnext');
var postcss = require('gulp-postcss');
var concat = require('gulp-concat');
var notify = require('gulp-notify');
var stylus = require('gulp-stylus');

gulp.task('css', function() {
  return gulp.src('*.styl')
    .pipe(stylus().on('error', error))
    .pipe(postcss([bemLinter()]).on('error', error))
    .pipe(concat('built.css'))
    .pipe(postcss([atImport(), cssnext()]))
    .pipe(gulp.dest('./built'));
});