Update topbar layout and styling in App.tsx

client/src/App.tsx

@@ -13,6 +13,7 @@ export default function App() {
   return (
     <div className="app-shell">
       <header className="topbar">
+        <div className="container topbar-inner">
           <NavLink to="/" className="brand">
             IG Japanese Quizzer
           </NavLink>
@@ -20,10 +21,11 @@ export default function App() {
             <NavLink to="/" end className={({ isActive }) => (isActive ? 'link active' : 'link')}>
               Overview
             </NavLink>
-          <button className="link" onClick={startRandomQuiz}>
+            <button className="link nav-link-btn" onClick={startRandomQuiz}>
               New Random Quiz
             </button>
           </nav>
+        </div>
       </header>
 
       <main className="main">