gulp-css-top.js

gulp.task('css', function(){
   gulp.src('css/*.css')
   .pipe(uncss({
       html: ['*.html'],
       js: ['*.js']
   }))
   .pipe(cleanCSS({debug: true}, function(details) {
       console.log(details.name + ': ' + details.stats.originalSize);
       console.log(details.name + ': ' + details.stats.minifiedSize);
   }))
   .pipe(concat('master.min.css'))
   .pipe(gulp.dest('css'));
});