Eleventy: Minify CSS and overwrite file (without inline integration)

.eleventy.js

module.exports = function (eleventyConfig) {

// npm install --save-dev clean-css
    eleventyConfig.on('afterBuild', () => {
        const CleanCSS = require("clean-css");
        const fs = require('fs');

        // Run me after the build ends
        var inputFile = 'src/assets/css/main.css';
        var input = fs.readFileSync(inputFile, 'utf8');
        var output = new CleanCSS().minify(input);
        fs.writeFile('_site/assets/css/main.css', output.styles, function (err) {
            if (err) return console.log('Error minifying main.css' + err);
            //success
          });
    });
}

// if you want to use inline styles, see: https://www.11ty.dev/docs/quicktips/inline-css/