Add system font stack to base CSS

Updated the base CSS to use a system font stack for improved typography and consistency across platforms.

Author: Mqxx

deno.lock

@@ -4,4 +4,5 @@
   margin: 0;
   padding: 0;
   color-scheme: dark;
+  font-family: system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, 'Open Sans', 'Helvetica Neue', sans-serif;
 }