Compile all css files into one css file in gulp

Question

I'm trying to learn Gulp. Got a gulp watch fine and can easily compile scss to css. This is all working.

I am stuck now though.... How can I compile multiple css files into one css file?

I am currently using:

gulp.task('styles', function () {
  return gulp.src('app/css/*.css')
    .pipe(concatCss('styles/bundle.css'))
    .pipe(gulp.dest('dist/css'));
});

But it's not working. All that keeps happening is my app files (main.css and section.css) are output in my dist folder (this is correct) but not in one file. They are just simply compied instead of both being compiled into a styles.css file for example.

Thank you for any suggestions. As I say, I am trying to learn Gulp. I thought I had been doing well until this.