gulpfile.js

var gulp = require('gulp');
var bs = require('browser-sync').create();
var reload = bs.reload;

// watch files for changes and reload
gulp.task('watch', function(gulpCallback) {

    // bs.init
    bs.init({
        proxy: "example.dev"
    });

    // watch php and reload browsers when it changes
    gulp.watch('**/*.php', reload);

    // grab css files and send them into bs.stream
    gulp.watch('**/*.css', function() {
        // this injects the css into the page
        gulp.src('**/*.css')
            .pipe(bs.stream());
    });

    // notify gulp that this task is done
    gulpCallback();
});