How to use autoprefixer with Gulp?

Question

I am trying this code on the gulpfile.js and it generates the directory and file but does not add the prefixes shown on the autoprefixer website. What am I doing wrong?

const gulp = require('gulp');
const autoprefixer = require('gulp-autoprefixer');

exports.styles = () => (
    gulp.src('css/styles.css')
        .pipe(autoprefixer())
        .pipe(gulp.dest('build'))
);