diff --git a/frontend/app/api/config/route.ts b/frontend/app/api/config/route.ts
new file mode 100644
index 00000000..ee979ac3
--- /dev/null
+++ b/frontend/app/api/config/route.ts
@@ -0,0 +1,11 @@
+/**
+ * API route to expose public configuration
+ * This allows environment variables to be loaded at runtime instead of build time
+ */
+import { NextResponse } from "next/server";
+
+export async function GET() {
+  return NextResponse.json({
+    googleClientId: process.env.NEXT_PUBLIC_GOOGLE_CLIENT_ID || "",
+  });
+}
diff --git a/frontend/components/auth/login-button.tsx b/frontend/components/auth/login-button.tsx
index ca6a60fe..3b80b60a 100644
--- a/frontend/components/auth/login-button.tsx
+++ b/frontend/components/auth/login-button.tsx
@@ -53,7 +53,11 @@ export function LoginButton() {
     return (
       <DropdownMenu>
         <DropdownMenuTrigger asChild>
-          <Button variant="outline" size="sm" className="gap-2">
+          <Button 
+            variant="ghost" 
+            size="sm" 
+            className="gap-2 bg-white/20 hover:bg-white/30 text-white border-white/30 border"
+          >
             {user.avatar_url ? (
               <img
                 src={user.avatar_url}
@@ -66,7 +70,7 @@ export function LoginButton() {
             <span className="hidden sm:inline max-w-[100px] truncate">
               {user.name || user.email}
             </span>
-            <Cloud className="w-3 h-3 text-green-500" />
+            <Cloud className="w-3 h-3 text-green-300" />
           </Button>
         </DropdownMenuTrigger>
         <DropdownMenuContent align="end" className="w-56">
@@ -90,10 +94,15 @@ export function LoginButton() {
   }
 
   return (
-    <Button variant="outline" size="sm" onClick={login} className="gap-2">
+    <Button 
+      variant="ghost" 
+      size="sm" 
+      onClick={login} 
+      className="gap-2 bg-white/20 hover:bg-white/30 text-white border-white/30 border"
+    >
       <GoogleIcon />
       <span className="hidden sm:inline">登入</span>
-      <CloudOff className="w-3 h-3 text-gray-400 sm:hidden" />
+      <CloudOff className="w-3 h-3 text-white/60 sm:hidden" />
     </Button>
   );
 }
diff --git a/frontend/contexts/auth-context.tsx b/frontend/contexts/auth-context.tsx
index bcbd8a28..3bced31d 100644
--- a/frontend/contexts/auth-context.tsx
+++ b/frontend/contexts/auth-context.tsx
@@ -31,12 +31,6 @@ const AuthContext = createContext<AuthContextType | undefined>(undefined);
 // Token storage key
 const TOKEN_KEY = "tradingagents_auth_token";
 
-// Google OAuth client ID from environment
-const GOOGLE_CLIENT_ID = process.env.NEXT_PUBLIC_GOOGLE_CLIENT_ID || "";
-
-// Backend URL
-const BACKEND_URL = process.env.NEXT_PUBLIC_API_URL || "";
-
 /**
  * Auth Provider Component
  */
@@ -44,6 +38,19 @@ export function AuthProvider({ children }: { children: ReactNode }) {
   const [user, setUser] = useState<User | null>(null);
   const [token, setToken] = useState<string | null>(null);
   const [isLoading, setIsLoading] = useState(true);
+  const [googleClientId, setGoogleClientId] = useState<string>("");
+
+  // Fetch Google Client ID from API (runtime)
+  useEffect(() => {
+    fetch("/api/config")
+      .then(res => res.json())
+      .then(data => {
+        setGoogleClientId(data.googleClientId || "");
+      })
+      .catch(err => {
+        console.error("Failed to fetch config:", err);
+      });
+  }, []);
 
   // Parse JWT token to get user info
   const parseToken = useCallback((token: string): User | null => {
@@ -102,7 +109,7 @@ export function AuthProvider({ children }: { children: ReactNode }) {
 
   // Login - redirect to Google OAuth
   const login = useCallback(() => {
-    if (!GOOGLE_CLIENT_ID) {
+    if (!googleClientId) {
       console.error("Google Client ID not configured");
       alert("Google 登入尚未設定。請聯繫管理員。");
       return;
@@ -113,7 +120,7 @@ export function AuthProvider({ children }: { children: ReactNode }) {
     const scope = "openid email profile";
     
     const params = new URLSearchParams({
-      client_id: GOOGLE_CLIENT_ID,
+      client_id: googleClientId,
       redirect_uri: redirectUri,
       response_type: "code",
       scope: scope,
@@ -122,7 +129,7 @@ export function AuthProvider({ children }: { children: ReactNode }) {
     });
 
     window.location.href = `https://accounts.google.com/o/oauth2/v2/auth?${params.toString()}`;
-  }, []);
+  }, [googleClientId]);
 
   // Logout
   const logout = useCallback(() => {