Migrate CSS files to subdirectory

assets/css/global.css

@@ -1,5 +1,6 @@
 @import url('https://fonts.googleapis.com/css2?family=Inter:ital,opsz,wght@0,14..32,100..900;1,14..32,100..900&display=swap');
 @import url('navigation.css');
+
 body {
     background-color: white;
     font-family: 'Inter', sans-serif;