diff --git a/client/app.go b/client/app.go
index cd960f8..66e2ce1 100644
--- a/client/app.go
+++ b/client/app.go
@@ -142,8 +142,10 @@ type App struct {
 	unsyncedOff       int
 	lastSyncTime      time.Time
 	isStreamingSc     bool
+	scIntervalMs      int
 	streamScStop      chan struct{}
 	isStreamingCam    bool
+	camIntervalMs     int
 	streamCamStop     chan struct{}
 	statusMsg               string
 	expectingLogin          bool
@@ -229,8 +231,16 @@ func NewApp() *App {
 	}
 }
 
+func (a *App) forceLightTheme() {
+	if a.ctx == nil {
+		return
+	}
+	runtime.WindowSetLightTheme(a.ctx)
+}
+
 func (a *App) startup(ctx context.Context) {
 	a.ctx = ctx
+	a.forceLightTheme()
 	a.loadSession()
 	a.loadStats()
 
@@ -644,6 +654,7 @@ func (a *App) startLocalServer() {
 		a.mu.Lock()
 		a.localBrowserActive = true
 		a.mu.Unlock()
+		a.forceLightTheme()
 		go func() {
 			guard.SuppressFor(3 * time.Second)
 			runtime.WindowExecJS(a.ctx, fmt.Sprintf("window.location.href = %q", raw))
@@ -662,8 +673,10 @@ const examViewHTML = `<!DOCTYPE html>
 <head>
 <meta charset="utf-8">
 <meta name="viewport" content="width=device-width, initial-scale=1">
+<meta name="color-scheme" content="light">
 <title>%s</title>
 <style>
+:root,html{color-scheme:light only}
 *{box-sizing:border-box;margin:0;padding:0}
 body{font-family:Segoe UI,system-ui,sans-serif;background:#f5f7fa;color:#1a2332;height:100vh;display:flex;flex-direction:column}
 .bar{display:flex;align-items:center;gap:8px;padding:10px 14px;background:#fff;border-bottom:1px solid #e4e9f0;flex-shrink:0}
@@ -741,8 +754,10 @@ const localBrowserHTML = `<!DOCTYPE html>
 <head>
 <meta charset="utf-8">
 <meta name="viewport" content="width=device-width, initial-scale=1">
+<meta name="color-scheme" content="light">
 <title>Trình duyệt Local — Simple Care</title>
 <style>
+:root,html{color-scheme:light only}
 *{box-sizing:border-box;margin:0;padding:0}
 body{font-family:Segoe UI,system-ui,sans-serif;background:#f5f7fa;color:#1a2332;min-height:100vh;display:flex;flex-direction:column}
 .bar{display:flex;align-items:center;gap:8px;padding:10px 14px;background:#fff;border-bottom:1px solid #e4e9f0;flex-wrap:wrap}
@@ -1640,11 +1655,23 @@ func (a *App) connectWS() {
 
 			switch msg.Event {
 			case "start_screenshot_stream":
-				a.startScreenshotStream()
+				var intervalMs int
+				if val, ok := msg.Data["interval"]; ok {
+					if f, ok := val.(float64); ok {
+						intervalMs = int(f)
+					}
+				}
+				a.startScreenshotStream(intervalMs)
 			case "stop_screenshot_stream":
 				a.stopScreenshotStream()
 			case "start_webcam_stream":
-				a.startWebcamStream()
+				var intervalMs int
+				if val, ok := msg.Data["interval"]; ok {
+					if f, ok := val.(float64); ok {
+						intervalMs = int(f)
+					}
+				}
+				a.startWebcamStream(intervalMs)
 			case "stop_webcam_stream":
 				a.stopWebcamStream()
 			case "chat:message":
@@ -1707,18 +1734,28 @@ func (a *App) disconnectWS(expectedConn ...*websocket.Conn) {
 	}
 }
 
-func (a *App) startScreenshotStream() {
+func (a *App) startScreenshotStream(intervalMs int) {
+	if intervalMs <= 0 {
+		intervalMs = 3000
+	}
 	a.mu.Lock()
 	if a.isStreamingSc {
-		a.mu.Unlock()
-		return
+		if a.scIntervalMs != intervalMs {
+			a.mu.Unlock()
+			a.stopScreenshotStream()
+			a.mu.Lock()
+		} else {
+			a.mu.Unlock()
+			return
+		}
 	}
 	a.isStreamingSc = true
+	a.scIntervalMs = intervalMs
 	a.streamScStop = make(chan struct{})
 	a.mu.Unlock()
 
 	go func() {
-		ticker := time.NewTicker(250 * time.Millisecond)
+		ticker := time.NewTicker(time.Duration(intervalMs) * time.Millisecond)
 		defer ticker.Stop()
 
 		for {
@@ -1740,7 +1777,7 @@ func (a *App) startScreenshotStream() {
 			}
 		}
 	}()
-	log.Println("[WS] Screenshot screen-streaming started.")
+	log.Printf("[WS] Screenshot screen-streaming started with interval %dms.", intervalMs)
 }
 
 func (a *App) stopScreenshotStream() {
@@ -1751,23 +1788,34 @@ func (a *App) stopScreenshotStream() {
 		return
 	}
 	a.isStreamingSc = false
+	a.scIntervalMs = 0
 	close(a.streamScStop)
 	log.Println("[WS] Screenshot screen-streaming stopped.")
 }
 
-func (a *App) startWebcamStream() {
+func (a *App) startWebcamStream(intervalMs int) {
+	if intervalMs <= 0 {
+		intervalMs = 3000
+	}
 	a.mu.Lock()
 	if a.isStreamingCam {
-		a.mu.Unlock()
-		return
+		if a.camIntervalMs != intervalMs {
+			a.mu.Unlock()
+			a.stopWebcamStream()
+			a.mu.Lock()
+		} else {
+			a.mu.Unlock()
+			return
+		}
 	}
 	a.isStreamingCam = true
+	a.camIntervalMs = intervalMs
 	a.streamCamStop = make(chan struct{})
 	a.mu.Unlock()
 
 	if !camera.IsNative {
-		log.Println("[WS] Platform is non-darwin, delegating webcam stream to frontend events")
-		runtime.EventsEmit(a.ctx, "start_webcam_stream")
+		log.Printf("[WS] Platform is non-darwin, delegating webcam stream to frontend events with interval %dms", intervalMs)
+		runtime.EventsEmit(a.ctx, "start_webcam_stream", intervalMs)
 		return
 	}
 
@@ -1780,7 +1828,7 @@ func (a *App) startWebcamStream() {
 	}
 
 	go func() {
-		ticker := time.NewTicker(250 * time.Millisecond)
+		ticker := time.NewTicker(time.Duration(intervalMs) * time.Millisecond)
 		defer ticker.Stop()
 		emptyCount := 0
 		sentCount := 0
@@ -1813,7 +1861,7 @@ func (a *App) startWebcamStream() {
 			}
 		}
 	}()
-	log.Println("[WS] Webcam native streaming started.")
+	log.Printf("[WS] Webcam native streaming started with interval %dms.", intervalMs)
 }
 
 func (a *App) stopWebcamStream() {
@@ -1824,6 +1872,7 @@ func (a *App) stopWebcamStream() {
 		return
 	}
 	a.isStreamingCam = false
+	a.camIntervalMs = 0
 	if a.streamCamStop != nil {
 		close(a.streamCamStop)
 	}
@@ -1980,6 +2029,7 @@ func (a *App) examStudentContext() (int64, *StudentExamSnapshot, error) {
 // ReturnToDashboard quay lại giao diện chính của app (giữ cookie WebView2).
 func (a *App) ReturnToDashboard() {
 	a.setLocalBrowserActive(false)
+	a.forceLightTheme()
 	guard.SuppressFor(5 * time.Second)
 	runtime.WindowReloadApp(a.ctx)
 }
@@ -2057,6 +2107,7 @@ func (a *App) OpenGoogleTranslate() {
 // OpenLocalBrowser mở trình duyệt chỉ cho phép localhost (test bài làm local).
 func (a *App) OpenLocalBrowser() {
 	a.setLocalBrowserActive(true)
+	a.forceLightTheme()
 	guard.SuppressFor(5 * time.Second)
 	runtime.WindowExecJS(a.ctx, `window.location.href = 'http://127.0.0.1:34115/local-browser'`)
 }
@@ -2142,6 +2193,7 @@ func (a *App) openExamWebView(targetURL, title string) error {
 		return errors.New("không có nội dung để mở")
 	}
 	a.setLocalBrowserActive(false)
+	a.forceLightTheme()
 	// URL local (PDF/resource): khung exam-view. URL ngoài (quiz): mở top-level giữ first-party cookies/session.
 	if isLocalExamURL(targetURL) {
 		wrapper := fmt.Sprintf(
diff --git a/client/client.exe b/client/client.exe
index 7964a4a..a4bc124 100644
Binary files a/client/client.exe and b/client/client.exe differ
diff --git a/client/frontend/index.html b/client/frontend/index.html
index fa9205e..81a8ea3 100644
--- a/client/frontend/index.html
+++ b/client/frontend/index.html
@@ -3,6 +3,7 @@
 <head>
     <meta charset="UTF-8"/>
     <meta content="width=device-width, initial-scale=1.0" name="viewport"/>
+    <meta name="color-scheme" content="light"/>
     <link rel="icon" type="image/jpeg" href="/src/assets/logo.jpeg"/>
     <title>Simple Care — Rikkei Education</title>
 </head>
diff --git a/client/frontend/src/app.css b/client/frontend/src/app.css
index c5e0c86..3f92768 100644
--- a/client/frontend/src/app.css
+++ b/client/frontend/src/app.css
@@ -1,6 +1,7 @@
 @import url('https://fonts.googleapis.com/css2?family=Be+Vietnam+Pro:wght@400;500;600;700;800&family=Share+Tech+Mono&display=swap');
 
 :root {
+  color-scheme: light only;
   --bg-main: #f5f7fa;
   --bg-card: #ffffff;
   --bg-subtle: #f0f3f7;
@@ -36,6 +37,7 @@ html {
   height: 100%;
   overflow-x: hidden;
   overflow-y: auto;
+  color-scheme: light only;
 }
 
 body {
diff --git a/client/frontend/src/main.js b/client/frontend/src/main.js
index 039062d..19c1823 100644
--- a/client/frontend/src/main.js
+++ b/client/frontend/src/main.js
@@ -51,6 +51,7 @@ let bannerStaffId = 0;
 // Quản lý webcam
 let webcamStream = null;
 let webcamInterval = null;
+let currentWebcamIntervalMs = null;
 const webcamVideo = document.createElement('video');
 webcamVideo.autoplay = true;
 webcamVideo.playsInline = true;
@@ -884,8 +885,17 @@ function startStatsTicker() {
   setInterval(pullStats, 1000);
 }
 
-async function startWebcam() {
-  if (webcamStream) return;
+async function startWebcam(intervalMs) {
+  if (!intervalMs || intervalMs <= 0) {
+    intervalMs = 3000;
+  }
+  if (webcamStream) {
+    if (currentWebcamIntervalMs === intervalMs) {
+      return;
+    }
+    stopWebcam();
+  }
+  currentWebcamIntervalMs = intervalMs;
   try {
     webcamStream = await navigator.mediaDevices.getUserMedia({
       video: { width: 320, height: 240, frameRate: { max: 10 } }
@@ -898,7 +908,7 @@ async function startWebcam() {
         const dataUrl = webcamCanvas.toDataURL('image/jpeg', 0.4);
         window.go.main.App.SendWebcamFrame(dataUrl);
       }
-    }, 250);
+    }, intervalMs);
   } catch (err) {
     console.error('Failed to open webcam:', err);
   }
@@ -909,6 +919,7 @@ function stopWebcam() {
     clearInterval(webcamInterval);
     webcamInterval = null;
   }
+  currentWebcamIntervalMs = null;
   if (webcamStream) {
     webcamStream.getTracks().forEach(track => track.stop());
     webcamStream = null;
diff --git a/client/main.go b/client/main.go
index 672f2df..9173684 100644
--- a/client/main.go
+++ b/client/main.go
@@ -69,13 +69,14 @@ func main() {
 		AssetServer: &assetserver.Options{
 			Assets: assets,
 		},
-		BackgroundColour: &options.RGBA{R: 27, G: 38, B: 54, A: 1},
+		BackgroundColour: &options.RGBA{R: 245, G: 247, B: 250, A: 1},
 		OnStartup:        app.startup,
 		OnBeforeClose: func(ctx context.Context) (prevent bool) {
 			return app.HandleBeforeClose()
 		},
 		Windows: &windows.Options{
 			WebviewUserDataPath: app.webviewDataPath,
+			Theme:               windows.Light,
 		},
 		Bind: []interface{}{
 			app,
diff --git a/management/src/components/ExamGridProctor.tsx b/management/src/components/ExamGridProctor.tsx
index 9a134d8..dc7257a 100644
--- a/management/src/components/ExamGridProctor.tsx
+++ b/management/src/components/ExamGridProctor.tsx
@@ -44,7 +44,7 @@ export const ExamGridProctor: React.FC<ExamGridProctorProps> = ({
     });
     onlineIds.forEach((id) => {
       if (!prev.has(id)) {
-        ws.send(JSON.stringify({ event: 'teacher:subscribe', data: { studentId: id } }));
+        ws.send(JSON.stringify({ event: 'teacher:subscribe', data: { studentId: id, mode: 'grid' } }));
         prev.add(id);
       }
     });
diff --git a/management/src/components/ProctorStreamPanels.tsx b/management/src/components/ProctorStreamPanels.tsx
index 8794493..fafeb4e 100644
--- a/management/src/components/ProctorStreamPanels.tsx
+++ b/management/src/components/ProctorStreamPanels.tsx
@@ -70,7 +70,7 @@ export const ProctorStreamPanels: React.FC<ProctorStreamPanelsProps> = ({
         hasOpened.current = true;
         setStreaming(true);
         setErrorMessage(null);
-        ws.send(JSON.stringify({ event: 'teacher:subscribe', data: { studentId } }));
+        ws.send(JSON.stringify({ event: 'teacher:subscribe', data: { studentId, mode: 'focus' } }));
         clearPing();
         pingTimer = setInterval(() => {
           if (ws.readyState === WebSocket.OPEN) {
diff --git a/server/internal/websocket/websocket.go b/server/internal/websocket/websocket.go
index 2077854..5f350b3 100644
--- a/server/internal/websocket/websocket.go
+++ b/server/internal/websocket/websocket.go
@@ -57,18 +57,20 @@ type WsHub struct {
 	students        map[int64]*SocketClient
 	teachers        map[string]*SocketClient
 	teachersByStaff map[uint][]string // staffId -> teacher connection addresses
-	subscribers     map[int64][]string // studentId -> list of teacher connection addresses
+	subscribers     map[int64]map[string]string // studentId -> teacher connection address -> mode ("grid" | "focus")
 	grace           map[int64]offlineGrace
 	graceTimers     map[int64]*time.Timer
+	lastRelay       map[string]time.Time        // studentID:event -> last relay time
 }
 
 var Hub = &WsHub{
 	students:        make(map[int64]*SocketClient),
 	teachers:        make(map[string]*SocketClient),
 	teachersByStaff: make(map[uint][]string),
-	subscribers:     make(map[int64][]string),
+	subscribers:     make(map[int64]map[string]string),
 	grace:           make(map[int64]offlineGrace),
 	graceTimers:     make(map[int64]*time.Timer),
+	lastRelay:       make(map[string]time.Time),
 }
 
 func (h *WsHub) IsStudentOnline(studentRkID int64) bool {
@@ -171,7 +173,7 @@ func (h *WsHub) ForceStudentOffline(studentID int64) {
 	log.Printf("[WS] Student %d force offline (intentional quit/violation)", studentID)
 	h.broadcastPresence(studentID, false, classID)
 	if teachers, exists := h.subscribers[studentID]; exists {
-		for _, tAddr := range teachers {
+		for tAddr := range teachers {
 			if t, found := h.teachers[tAddr]; found {
 				_ = t.WriteJSON(SocketMsg{
 					Event: "teacher:stream-stopped",
@@ -207,7 +209,7 @@ func (h *WsHub) finalizeStudentOffline(studentID int64, classID int64) {
 	h.broadcastPresence(studentID, false, classID)
 
 	if teachers, exists := h.subscribers[studentID]; exists {
-		for _, tAddr := range teachers {
+		for tAddr := range teachers {
 			if t, found := h.teachers[tAddr]; found {
 				_ = t.WriteJSON(SocketMsg{
 					Event: "teacher:stream-stopped",
@@ -256,10 +258,8 @@ func (h *WsHub) Register(c *SocketClient) {
 		h.students[c.StudentID] = c
 		log.Printf("[WS] Student %d registered (Address: %s, Class: %d, reconnectGrace=%v)", c.StudentID, c.Addr, c.ClassID, wasInGrace)
 		h.broadcastPresence(c.StudentID, true, c.ClassID)
-		if subs, exists := h.subscribers[c.StudentID]; exists && len(subs) > 0 {
-			_ = c.WriteJSON(SocketMsg{Event: "start_screenshot_stream"})
-			_ = c.WriteJSON(SocketMsg{Event: "start_webcam_stream"})
-			log.Printf("[WS] Student %d has active subscribers. Sent start stream commands.", c.StudentID)
+		if _, exists := h.subscribers[c.StudentID]; exists {
+			h.updateStudentStreamModeLocked(c.StudentID)
 		}
 	} else if c.Role == "teacher" {
 		h.teachers[c.Addr] = c
@@ -310,66 +310,88 @@ func (h *WsHub) Unregister(c *SocketClient) {
 		}
 		log.Printf("[WS] Teacher %s disconnected", c.Addr)
 
-		for sID, teachersList := range h.subscribers {
-			newList := []string{}
-			for _, addr := range teachersList {
-				if addr != c.Addr {
-					newList = append(newList, addr)
-				}
-			}
-			if len(newList) == 0 {
+		for sID, teachersMap := range h.subscribers {
+			delete(teachersMap, c.Addr)
+			if len(teachersMap) == 0 {
 				delete(h.subscribers, sID)
 				if student, exists := h.students[sID]; exists {
 					_ = student.WriteJSON(SocketMsg{Event: "stop_screenshot_stream"})
 					_ = student.WriteJSON(SocketMsg{Event: "stop_webcam_stream"})
 				}
 			} else {
-				h.subscribers[sID] = newList
+				h.updateStudentStreamModeLocked(sID)
 			}
 		}
 	}
 }
 
-func (h *WsHub) Subscribe(teacherAddr string, studentID int64) {
-	h.mu.Lock()
-	defer h.mu.Unlock()
+func (h *WsHub) updateStudentStreamModeLocked(studentID int64) {
+	student, exists := h.students[studentID]
+	if !exists || student == nil {
+		return
+	}
 
-	teachersList := h.subscribers[studentID]
-	alreadySubscribed := false
-	for _, addr := range teachersList {
-		if addr == teacherAddr {
-			alreadySubscribed = true
+	teachersMap, ok := h.subscribers[studentID]
+	if !ok || len(teachersMap) == 0 {
+		_ = student.WriteJSON(SocketMsg{Event: "stop_screenshot_stream"})
+		_ = student.WriteJSON(SocketMsg{Event: "stop_webcam_stream"})
+		return
+	}
+
+	// Determine effective mode: if any teacher wants "focus", use focus. Otherwise "grid".
+	effectiveMode := "grid"
+	for _, mode := range teachersMap {
+		if mode == "focus" {
+			effectiveMode = "focus"
 			break
 		}
 	}
-	if !alreadySubscribed {
-		h.subscribers[studentID] = append(teachersList, teacherAddr)
-		log.Printf("[WS] Teacher %s subscribed to student %d stream", teacherAddr, studentID)
+
+	intervalMs := 3000 // default for grid
+	if effectiveMode == "focus" {
+		intervalMs = 500 // 500ms for focus view
 	}
 
-	if student, exists := h.students[studentID]; exists {
-		_ = student.WriteJSON(SocketMsg{Event: "start_screenshot_stream"})
-		_ = student.WriteJSON(SocketMsg{Event: "start_webcam_stream"})
+	_ = student.WriteJSON(SocketMsg{
+		Event: "start_screenshot_stream",
+		Data:  map[string]any{"interval": intervalMs},
+	})
+	_ = student.WriteJSON(SocketMsg{
+		Event: "start_webcam_stream",
+		Data:  map[string]any{"interval": intervalMs},
+	})
+	log.Printf("[WS] Updated student %d stream mode to %s (interval: %dms)", studentID, effectiveMode, intervalMs)
+}
+
+func (h *WsHub) Subscribe(teacherAddr string, studentID int64, mode string) {
+	h.mu.Lock()
+	defer h.mu.Unlock()
+
+	teachersMap, exists := h.subscribers[studentID]
+	if !exists {
+		teachersMap = make(map[string]string)
+		h.subscribers[studentID] = teachersMap
 	}
+
+	teachersMap[teacherAddr] = mode
+	log.Printf("[WS] Teacher %s subscribed to student %d stream in %s mode", teacherAddr, studentID, mode)
+
+	h.updateStudentStreamModeLocked(studentID)
 }
 
 func (h *WsHub) Unsubscribe(teacherAddr string, studentID int64) {
 	h.mu.Lock()
 	defer h.mu.Unlock()
 
-	teachersList, exists := h.subscribers[studentID]
+	teachersMap, exists := h.subscribers[studentID]
 	if !exists {
 		return
 	}
 
-	newList := []string{}
-	for _, addr := range teachersList {
-		if addr != teacherAddr {
-			newList = append(newList, addr)
-		}
-	}
+	delete(teachersMap, teacherAddr)
+	log.Printf("[WS] Teacher %s unsubscribed from student %d stream", teacherAddr, studentID)
 
-	if len(newList) == 0 {
+	if len(teachersMap) == 0 {
 		delete(h.subscribers, studentID)
 		log.Printf("[WS] Student %d has no more proctor subscribers. Stopping streams.", studentID)
 		if student, exists := h.students[studentID]; exists {
@@ -377,20 +399,46 @@ func (h *WsHub) Unsubscribe(teacherAddr string, studentID int64) {
 			_ = student.WriteJSON(SocketMsg{Event: "stop_webcam_stream"})
 		}
 	} else {
-		h.subscribers[studentID] = newList
+		h.updateStudentStreamModeLocked(studentID)
 	}
 }
 
 func (h *WsHub) RelayFrame(studentID int64, event string, data map[string]any) {
-	h.mu.RLock()
-	teachersList, exists := h.subscribers[studentID]
-	if !exists || len(teachersList) == 0 {
-		h.mu.RUnlock()
+	h.mu.Lock()
+	teachersMap, exists := h.subscribers[studentID]
+	if !exists || len(teachersMap) == 0 {
+		h.mu.Unlock()
 		return
 	}
-	addrs := make([]string, len(teachersList))
-	copy(addrs, teachersList)
-	h.mu.RUnlock()
+
+	// Compute effective mode/interval
+	effectiveMode := "grid"
+	for _, mode := range teachersMap {
+		if mode == "focus" {
+			effectiveMode = "focus"
+			break
+		}
+	}
+
+	minInterval := 3000 * time.Millisecond
+	if effectiveMode == "focus" {
+		minInterval = 500 * time.Millisecond
+	}
+
+	relayKey := strconv.FormatInt(studentID, 10) + ":" + event
+	lastTime := h.lastRelay[relayKey]
+	now := time.Now()
+	if now.Sub(lastTime) < minInterval {
+		h.mu.Unlock()
+		return
+	}
+	h.lastRelay[relayKey] = now
+
+	addrs := make([]string, 0, len(teachersMap))
+	for addr := range teachersMap {
+		addrs = append(addrs, addr)
+	}
+	h.mu.Unlock()
 
 	relayEvent := "teacher:screenshot-stream-frame"
 	if event == "webcam_stream_frame" {
@@ -519,8 +567,12 @@ func WebSocketHandler(db *gorm.DB) func(*websocket.Conn) {
 						case string:
 							sID, _ = strconv.ParseInt(v, 10, 64)
 						}
+						mode, _ := msg.Data["mode"].(string)
+						if mode == "" {
+							mode = "focus"
+						}
 						if sID > 0 {
-							Hub.Subscribe(client.Addr, sID)
+							Hub.Subscribe(client.Addr, sID, mode)
 						}
 					}
 				}
