gulpfile.js

'use strict';
var gulp = require('gulp');
var livereload = require('gulp-livereload');
var prefix = require('gulp-autoprefixer');
var sourcemaps = require('gulp-sourcemaps');
var sass = require('gulp-sass');
var plumber = require('gulp-plumber');

gulp.task('styles', async function(cb) {
  await gulp.src('scss/style.scss')
    .pipe(sourcemaps.init())
    .pipe(sass({outputStyle: 'compressed'}).on('error', sass.logError))
    .pipe(plumber())
    .pipe(sourcemaps.write())
    .pipe(prefix("last 1 version", "> 1%", "ie 8", "ie 7"))
    .pipe(gulp.dest('css'));
  cb()
});

gulp.task('watch', function() {
  livereload.listen();
  gulp.watch(['css/**']).on('change', function() {
    var args = arguments;
    setTimeout(function() {
      livereload.changed.apply(this, args);
    }, 200);
  });
  gulp.watch(['scss/**/*'], gulp.series(['styles']));
});