style: enhance mobile nav menu with blur backdrop and improve heading semantics

src/styles/tailwind.css

@@ -38,6 +38,7 @@
   --animate-spin-reverse-slow: spin-reverse 4s linear infinite;
   --animate-spin-reverse-slower: spin-reverse 6s linear infinite;
   --animate-marquee-vertical: marquee-vertical 40s linear infinite;
+  --animate-bounce-y: bounce-y 1.5s infinite;
   
   --radius-4xl: 2rem;
   --radius-5xl: 2.5rem;
@@ -72,6 +73,17 @@
     }
   }
 
+  @keyframes bounce-y {
+    0%, 100% {
+      transform: translateY(-10%);
+      animation-timing-function: cubic-bezier(0.8, 0, 1, 1);
+    }
+    50% {
+      transform: translateY(0);
+      animation-timing-function: cubic-bezier(0, 0, 0.2, 1);
+    }
+  }
+
   @keyframes marquee-vertical {
     from {
       transform: translateY(0);