gulpfile.js

var gulp = require('gulp');
var concat = require('gulp-concat');
var sass = require('gulp-sass');
var minifyCss = require('gulp-minify-css');
var rename = require('gulp-rename');
var runSequence = require('run-sequence');

var paths = {
  sass: ['./scss/**/*.scss']
};

gulp.task('default', ['sass']);

gulp.task('serve:before', ['watch']);

gulp.task('sass', function(done) {
  gulp.src('./scss/ionic.app.scss')
    .pipe(sass())
    .on('error', sass.logError)
    .pipe(gulp.dest('./www/css/'))
    .pipe(minifyCss({
      keepSpecialComments: 0
    }))
    .pipe(rename({
      extname: '.min.css'
    }))
    .pipe(gulp.dest('./www/css/'))
    .on('end', done);
});

gulp.task('watch', function() {
  runSequence(
    ['sass'],
    function() {
      gulp.watch(paths.sass, ['sass']);
    }
  );
  gulp.watch(paths.sass, ['sass']);
});