postcss.config.js

let environment = {
    plugins: [
        require('autoprefixer'),
        require('postcss-import'),
        require('postcss-flexbugs-fixes'),
        require('postcss-preset-env')({
            autoprefixer: {
                flexbox: 'no-2009'
            },
            stage: 3
        }),
    ]
}

// Only run PurgeCSS in production (you can also add staging here)
// if (process.env.RAILS_ENV === "production") {
//     environment.plugins.push(
//         require('@fullhuman/postcss-purgecss')({
//             content: [
//                 './app/**/*.html.erb',
//                 './app/helpers/**/*.rb',
//                 './app/javascript/**/*.js',
//                 './app/javascript/**/*.vue',
//                 './app/javascript/**/*.jsx',
//             ],
//             defaultExtractor: content => content.match(/[A-Za-z0-9-_:/]+/g) || []
//         })
//     )
// }

module.exports = environment