Add visual feedback for unread messages in the menu. Implement a pulsing animation and color change for the inbox button when there are unread chats. Also, add sound notification for new messages received, enhancing user experience.

client/src/style.css

@@ -67,6 +67,24 @@ html, body, #app {
   background-color: #52a052;
 }
 
+.menu button.has-unread {
+  background-color: #ff6b6b;
+  animation: pulse 2s infinite;
+}
+
+.menu button.has-unread:hover {
+  background-color: #ff5252;
+}
+
+@keyframes pulse {
+  0%, 100% {
+    opacity: 1;
+  }
+  50% {
+    opacity: 0.8;
+  }
+}
+
 .menu span {
   display: inline-block;
   padding: 0.375em 0.4em;