Use CSS custom property for cleaner random animation delay

- Move animation-delay to CSS using custom property --random-delay
- JavaScript still required to generate random value (CSS has no random functions)
- Cleaner separation between styling (CSS) and logic (JavaScript)
- Maintains same functionality with better organization

examples/chat-ui/src/index.css

@@ -13,4 +13,5 @@
 
 .animated-hue-bg {
   animation: hue-rotate 60s linear infinite;
+  animation-delay: var(--random-delay, 0s);
 }