gulpfile.js

var gulp = require('gulp');

require('./tasks-css');
require('./tasks-js');
// etc.

gulp.task('dev', ['browsersync', 'html-watch', 'img-watch', 'css-watch', 'js-watch']);
gulp.task('dist', ['clean', 'html-compile', 'img-optimize', 'css-compile', 'js-transpile']);
// etc.

tasks-css.js

var config       = require('./config');
var gulp         = require('gulp');
var watch        = require('gulp-watch');
var sass         = require('gulp-sass');
var sourcemaps   = require('gulp-sourcemaps');
var postcss      = require('gulp-postcss');
var autoprefixer = require('autoprefixer');

/**
 * Task: CSS Compile
 */
gulp.task('css-compile', function() {
    gulp.src(config.paths.css.globStatic)
        .pipe(sourcemaps.init())
        .pipe(sass().on('error', sass.logError))
        .pipe(postcss([autoprefixer()]]))
        .pipe(minifyCss())
        .pipe(sourcemaps.write('.'))
        .pipe(gulp.dest(config.paths.css.dirDist));
});

/**
 * Task: CSS Watch
 */
gulp.task('css-watch', ['css-compile'], function() {
    watch([config.paths.css.globWatch], function() {
        gulp.start(['css-compile']);
    });
});