[fix][x]: purge css in prod mode (#40)

postcss.config.js

@@ -1,4 +1,10 @@
-const tailwindcss = require('tailwindcss');
+const purgecss = [
+  '@fullhuman/postcss-purgecss',
+  {
+    content: ['./components/**/*.tsx', './pages/**/*.tsx'],
+    defaultExtractor: (content) => content.match(/[\w-/:]+(?<!:)/g) || [],
+  },
+];
 
 module.exports = {
   plugins: [
@@ -6,5 +12,6 @@ module.exports = {
     'postcss-import',
     'tailwindcss',
     'autoprefixer',
+    ...(process.env.NODE_ENV === 'production' ? [purgecss] : []),
   ],
 };