Minify CSS when mode is production

packages/next-css/css-loader-config.js

@@ -1,4 +1,5 @@
 const ExtractCssChunks = require('extract-css-chunks-webpack-plugin')
+const OptimizeCSSAssetsPlugin = require('optimize-css-assets-webpack-plugin')
 const findUp = require('find-up')
 
 const fileExtensions = new Set()
@@ -48,6 +49,13 @@ module.exports = (
     extractCssInitialized = true
   }
 
+  if (config.mode === 'production') {
+    if (!Array.isArray(config.optimization.minimizer)) {
+      config.optimization.minimizer = []
+    }
+    config.optimization.minimizer.push(new OptimizeCSSAssetsPlugin({}))
+  }
+
   const postcssConfig = findUp.sync('postcss.config.js', {
     cwd: config.context
   })

packages/next-css/package.json

@@ -10,6 +10,7 @@
     "extracted-loader": "1.0.4",
     "find-up": "2.1.0",
     "ignore-loader": "0.1.2",
+    "optimize-css-assets-webpack-plugin": "^5.0.1",
     "postcss-loader": "3.0.0"
   },
   "devDependencies": {