feat(styles): one stylesheet source for react and svelte (#3350)

* feat(styles): create stylesheets for react and svelte based on one source

* refactor(styling): cleanup

* refactor(postcss): share a config

* refactor(postcss): replace env hack with env file

packages/svelte/vite.config.ts

@@ -2,7 +2,10 @@ import { sveltekit } from '@sveltejs/kit/vite';
 import type { UserConfig } from 'vite';
 
 const config: UserConfig = {
-  plugins: [sveltekit()]
+  plugins: [sveltekit()],
+  css: {
+    postcss: './../../tooling/postcss-config/'
+  }
 };
 
 export default config;