Vue CLI 3 + PurgeCSS

purgecss.js

/**
1) npm i -D purgecss @fullhuman/postcss-purgecss purgecss-webpack-plugin glob-all path
2) edit vue.config.js 
*/

/**
** vue.config.js
*/
const PurgecssPlugin = require('purgecss-webpack-plugin');
const glob = require('glob-all');
const path = require('path');
module.exports = {
  configureWebpack() {
    // Additional config to be merged
    let additionalConfig = {};
    // Production config
    if (process.env.NODE_ENV === 'production') {
      additionalConfig = {
        plugins: [
          new PurgecssPlugin({
            paths: glob.sync([
              path.join(__dirname, './public/index.html'),
              path.join(__dirname, './src/**/*.vue'),
              path.join(__dirname, './src/**/*.html'),
            ]),
          }),
        ],
      };
    }
    return additionalConfig;
  },
};