gulpfile.js

var gulp = require('gulp'),
    sass = require('gulp-sass'),
    notify = require('gulp-notify'),
    sourcemaps = require('gulp-sourcemaps'),
    autoprefixer = require('gulp-autoprefixer');

gulp.task('default', function () {
});

gulp.task('styles', function () {
    return gulp.src('./assets/scss/bootstrap-ninjaforms-3.scss')
        .pipe(sourcemaps.init())
        .pipe(sass({
            outputStyle: 'compressed'
        }).on('error', sass.logError))
        .pipe(autoprefixer('last 2 version'))
        .pipe(sourcemaps.write('.'))
        .pipe(gulp.dest('./assets/css'))
        .pipe(notify({message: 'Bootstrap NinjaForms 3 styles task complete', onLast: true}));
});