clean up postcss config

platform/ui/postcss.config.js

@@ -1,10 +1,7 @@
+const path = require('path');
 const tailwindcss = require('tailwindcss');
-const commonConfigs = require('../../postcss.config.js');
+const tailwindConfigPath = path.join(__dirname, 'tailwind.config.js');
 
 module.exports = {
-  ...commonConfigs,
-  plugins: [
-    tailwindcss('./src/gatsby-theme-docz/tailwind.js'),
-    require('autoprefixer'),
-  ],
+  plugins: [tailwindcss(tailwindConfigPath), require('autoprefixer')],
 };