npm install gulp-penthouse --save-dev

var gulp = require('gulp');
var criticalCss = require('gulp-penthouse');

gulp.task('critical-css', function () {
    return gulp.src('./styles.css')
        .pipe(criticalCss({
            out: 'critical.css',
            url: 'http://localhost:9000',
            width: 1300,
            height: 900,
            strict: true,
            userAgent: 'Mozilla/5.0 (compatible; Googlebot/2.1; +http://www.google.com/bot.html)'
        }))
        .pipe(gulp.dest('./dist/css/'));
});