Gulp 4 CSS to SCSS with watch

gulp-4-scss.js

const gulp = require('gulp'),
sass   = require('gulp-sass'),
concat = require('gulp-concat'),
prefix = require('gulp-autoprefixer'),
rename = require('gulp-rename');
plumber = require('gulp-plumber');

function css() {
    return gulp
      .src('./scss/**/*.scss')
      .pipe(plumber())
      .pipe(sass({ outputStyle: 'compressed' }).on('error', sass.logError))
      .pipe(prefix('last 2 versions'))
      .pipe(concat('main.css'))
    //   .pipe(gulp.dest('./'))
      .pipe(rename({ suffix: '.min' }))
      .pipe(gulp.dest('./'))
}

function watchFiles() {
    gulp.watch('./scss/**/*', css);
}

exports.watch = watchFiles;
exports.default = css;