Concatenate,auto-prefix and minify css files using gulp

gulp-css

let
    gulp = require('gulp'),
    concat = require('gulp-concat-css'),
    minify = require('gulp-clean-css'),
    prefix = require('gulp-autoprefixer');

let path = {
    src: './*.css',
    dest: './done/'
}

gulp.task('css', function () {
    return gulp.src(path.src)
        .pipe(concat('app.css'))
        .pipe(prefix({
            browsers: ['last 2 versions'],
            cascade: false
        }))
        .pipe(minify({
            compatibility: 'ie8'
        }))
        .pipe(gulp.dest(path.dest))
})