Refactor topbar styling and add nav-link-btn class

client/src/App.css

@@ -3,9 +3,6 @@
 }
 
 .topbar {
-  display: flex;
-  align-items: center;
-  justify-content: space-between;
   padding: 1.25rem 0;
   position: sticky;
   top: 0;
@@ -13,6 +10,12 @@
   backdrop-filter: blur(12px);
 }
 
+.topbar-inner {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+}
+
 .brand {
   font-weight: 800;
   letter-spacing: -0.01em;
@@ -33,6 +36,15 @@ nav {
   font-weight: 600;
 }
 
+.nav-link-btn {
+  border: none;
+  background: transparent;
+  padding: 0.55rem 0.85rem;
+  border-radius: 12px;
+  font-weight: 600;
+  cursor: pointer;
+}
+
 .link.active {
   background: rgba(0, 0, 0, 0.06);
   color: var(--accent);