When you build your code for production, you need to minify CSS to reduce your application's size. Gulpjs has various plugins to do that. I will show you how to use gulp-clean-css plugin to minify CSS code

You install gulp-clean-css plugin as devDependencies

npm install --save-dev gulp-clean-css

In the gulpfile.js, you import gulp, gulp-clean-css and create a task.

const { src, dest } = require("gulp");
const cleanCSS = require("gulp-clean-css");

const minifyCSS = () => {
  return src("src/styles/*.css").pipe(cleanCSS()).pipe(dest("dist/styles"));
};

exports.default = minifyCSS;

My task will minify all css file in src/styles directory and write them to dist/styles directory. In the src function, you can replace the asterisk with your file's name

Run gulp command

gulp

After the command finishes, you will see your minified CSS files in the dist/styles directory