Add way to pass fonts

examples/customer-segmentation-server/src/mcp-app.css

@@ -2,6 +2,9 @@
 :root {
   color-scheme: light dark;
 
+  /* Font families */
+  --font-sans: system-ui, -apple-system, sans-serif;
+
   /* Background colors */
   --color-background-primary: light-dark(#ffffff, #111827);
   --color-background-secondary: light-dark(#f9fafb, #1f2937);
@@ -33,6 +36,7 @@
 html, body {
   margin: 0;
   padding: 0;
+  font-family: var(--font-sans);
   color: var(--color-text-primary);
   overflow: hidden;
 }