Add CSS & Icons docs

postcss.config.cjs

@@ -6,6 +6,9 @@ const config = {
     require('postcss-preset-env'),
     require('autoprefixer'),
     require('postcss-extend-rule'),
+    process.env.NODE_ENV === 'development' && require('cssnano')({
+      preset: 'default',
+    })
   ],
 };