switch to sass and split global styles, rework heading css

svelte.config.js

@@ -1,3 +1,5 @@
+import { resolve } from 'node:path';
+
 import staticAdapter from '@sveltejs/adapter-static';
 import { mdsvex } from 'mdsvex';
 
@@ -19,6 +21,9 @@ const config = {
         // If your environment is not supported or you settled on a specific environment, switch out the adapter.
         // See https://kit.svelte.dev/docs/adapters for more information about adapters.
         adapter: staticAdapter(),
+        alias: {
+            '$styles': 'src/styles',
+        }
     }
 };