[refactor,#59][s]: move packages/portal => examples/catalog as per plan in #59.

What is currently packages/portal is example of a running portal and should move to examples (it will get replaced by an actual portal lib soon).

examples/catalog/postcss.config.js

@@ -0,0 +1,17 @@
+const purgecss = [
+  '@fullhuman/postcss-purgecss',
+  {
+    content: ['./components/**/*.tsx', './pages/**/*.tsx'],
+    defaultExtractor: (content) => content.match(/[\w-/:]+(?<!:)/g) || [],
+  },
+];
+
+module.exports = {
+  plugins: [
+    'postcss-preset-env',
+    'postcss-import',
+    'tailwindcss',
+    'autoprefixer',
+    ...(process.env.NODE_ENV === 'production' ? [purgecss] : []),
+  ],
+};