gulpfile.js

'use strict';

var gulp = require('gulp');
var sass = require('gulp-sass');
var browserSync = require('browser-sync').create();

gulp.task('sass', function(){
    return gulp.src('./css/*.scss')
    .pipe(sass().on('error', sass.logError))
    .pipe(gulp.dest('./css'))
    .pipe(browserSync.stream());
});

gulp.task('sass:watch', function(){
    gulp.watch('./css/*.scss', ['sass']);
});

gulp.task('browser-sync', function(){
    var files = [
        './*.html',
        './css/*.css',
        './js/*.js',
        './img/*.{png,jpg,gif}',
    ];

    browserSync.init(files, {
        server:  {
            baseDir: './'
        }
    });
});

gulp.task('default', gulp.series('browser-sync', function(){
    gulp.start('sass:watch');
}));