Why is gulp-autoprefixer not working?

Question

Building projects

Good afternoon!
Why might gulp-autoprefixer not work?
var autoprefixer = require('gulp-autoprefixer');
gulp.task('default', function () {
gulp.src('css/*.css')
.pipe(gulp.dest('app/css'))
.pipe(autoprefixer({
browsers: ['last 3 versions']
}));
});
All other components work fine!

Answer 1

The autoprefixer works after saving the files to the app/css folder
here is an example of a correct task

gulp.task('default', function () {
    return gulp.src('css/*.css')
        .pipe(autoprefixer({
            browsers: ['last 3 versions'],
            cascade: false
        }))
        .pipe(gulp.dest('app/css'));
});