fix: use sans-serif as fallback font

Author: amliu-jumptrading

src/app.css

@@ -1,8 +1,8 @@
 .app {
   /* radix tokens */
   --color-background: #070b14;
-  --default-font-family: "Inter Tight";
-  font-family: "Inter Tight";
+  --default-font-family: "Inter Tight", sans-serif;
+  font-family: "Inter Tight", sans-serif;
   font-display: optional;
   --scaling: 0.875;
   --cursor-button: pointer;