diff --git a/server/web/index.html b/server/web/index.html
index 4e7fbb8..357b01d 100644
--- a/server/web/index.html
+++ b/server/web/index.html
@@ -574,6 +574,14 @@
             color: #fff;
         }
         .confirm-modal-actions .danger-btn:hover { box-shadow: 0 4px 12px rgba(192, 57, 43, 0.4); transform: translateY(-1px); }
+        /* Info variant for the generic alert dialog (single OK button). */
+        .confirm-modal-content.info { border-color: rgba(230, 126, 34, 0.25); }
+        .confirm-modal-icon.info { background: rgba(230, 126, 34, 0.15); color: #e67e22; }
+        .confirm-modal-actions .primary-btn {
+            background: linear-gradient(135deg, #b9770e 0%, #e67e22 100%);
+            color: #fff;
+        }
+        .confirm-modal-actions .primary-btn:hover { box-shadow: 0 4px 12px rgba(230, 126, 34, 0.4); transform: translateY(-1px); }
 
         .device-grid {
             display: grid;
@@ -1974,6 +1982,23 @@
         </div>
     </div>
 
+    <!-- Generic alert / confirmation dialog. Replaces native alert()/confirm():
+         their button labels come from the browser locale (e.g. German on a
+         German system) and do not match the app. -->
+    <div class="modal-overlay" id="app-dialog" onclick="if(event.target===this)closeAppDialog(false)"
+         onkeydown="if(event.key==='Escape')closeAppDialog(false)">
+        <div class="confirm-modal-content" id="app-dialog-content" role="dialog" aria-modal="true"
+             aria-labelledby="app-dialog-title" aria-describedby="app-dialog-message">
+            <div class="confirm-modal-icon" id="app-dialog-icon"></div>
+            <h3 id="app-dialog-title">Notice</h3>
+            <p id="app-dialog-message"></p>
+            <div class="confirm-modal-actions">
+                <button class="cancel-btn" id="app-dialog-cancel" onclick="closeAppDialog(false)">Cancel</button>
+                <button class="danger-btn" id="app-dialog-ok" onclick="closeAppDialog(true)">OK</button>
+            </div>
+        </div>
+    </div>
+
     <script src="__BASE_PATH__/static/xterm.js"></script>
     <script src="__BASE_PATH__/static/xterm-fit.js"></script>
 
@@ -2703,7 +2728,7 @@
                         // mode=removed：历史记录已删除，刷新后卡片消失。
                         getDevices();
                     } else {
-                        alert(msg.msg || 'Failed to delete device');
+                        appAlert(msg.msg || 'Failed to delete device', 'Unable to Delete Device');
                     }
                     break;
                 case 'list_users_result':
@@ -3289,7 +3314,10 @@
             const existing = wall.sessions.get(l32);
             if (existing && existing.fullId !== id) {
                 // 两台设备的低 32 位相同：绝不能共用一个解码器。
-                if (!restoring) alert('Device ID collision (low 32 bits). Cannot open both on the same wall.');
+                if (!restoring) {
+                    appAlert('Device ID collision (low 32 bits). Cannot open both on the same wall.',
+                             'Device ID Collision');
+                }
                 return null;
             }
             const uid = 'w' + (wall.uidSeq++);
@@ -3311,11 +3339,11 @@
 
         function addWallTile(deviceId) {
             if (!serverCaps.multiWatch) {
-                alert('Screen Wall is not supported by this server');
+                appAlert('Screen Wall is not supported by this server.', 'Screen Wall Unavailable');
                 return;
             }
             if (wall.tiles.length >= WALL_MAX_TILES) {
-                alert('Wall is full (max ' + WALL_MAX_TILES + ' tiles)');
+                appAlert('Wall is full (max ' + WALL_MAX_TILES + ' tiles).', 'Screen Wall Full');
                 return;
             }
             const dev = devices.find(d => String(d.id) === String(deviceId));
@@ -3355,9 +3383,11 @@
             wallUpdateSidebarBadges();
         }
 
-        function clearWall() {
+        async function clearWall() {
             if (!wall.tiles.length) return;
-            if (!confirm('Close all tiles on the wall?')) return;
+            const ok = await appConfirm('Close all tiles on the wall?',
+                { title: 'Clear Screen Wall', okText: 'Clear' });
+            if (!ok) return;
             const tiles = wall.tiles.slice();
             wall.tiles = [];
             for (const tile of tiles) {
@@ -3569,8 +3599,8 @@
             const tile = wall.tiles.find(t => t.uid === uid);
             if (!tile) return;
             const dev = devices.find(d => String(d.id) === tile.deviceId);
-            if (!dev) { alert('Device not found'); return; }
-            if (!dev.online) { alert('Device is offline'); return; }
+            if (!dev) { appAlert('Device not found.', 'Device Not Found'); return; }
+            if (!dev.online) { appAlert('Device is offline.', 'Device Offline'); return; }
             const s = wall.sessions.get(tile.low32);
             if (s && s.status === 'offline') {
                 // 设备重新上线：离线时服务端已移除 watch，且 streams 条目被整体删除，
@@ -3609,12 +3639,13 @@
 
         function showWall() {
             if (!serverCaps.multiWatch) {
-                alert('Screen Wall requires a newer server with multi-view support.');
+                appAlert('Screen Wall requires a newer server with multi-view support.',
+                         'Screen Wall Unavailable');
                 return;
             }
             const compat = checkWebCodecs();
             if (!compat.supported) {
-                alert('Browser does not support H.264: ' + compat.reason);
+                appAlert('Browser does not support H.264: ' + compat.reason, 'H.264 Not Supported');
                 return;
             }
             if (!wallRestored) wallRestoreState();
@@ -4450,6 +4481,74 @@
             updateAdminButtons();
         }
 
+        // ===== In-app alert / confirmation dialog =====
+        // Native alert()/confirm() use the browser locale for their buttons
+        // (e.g. "Abbrechen"/"OK" on a German system) and ignore the app theme.
+        // Both now go through the same themed modal as the logout prompt.
+        const APP_DIALOG_ICONS = {
+            danger: '<svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round">' +
+                '<path d="M10.29 3.86L1.82 18a2 2 0 0 0 1.71 3h16.94a2 2 0 0 0 1.71-3L13.71 3.86a2 2 0 0 0-3.42 0z"/>' +
+                '<line x1="12" y1="9" x2="12" y2="13"/><line x1="12" y1="17" x2="12.01" y2="17"/></svg>',
+            info: '<svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round">' +
+                '<circle cx="12" cy="12" r="10"/><line x1="12" y1="16" x2="12" y2="12"/>' +
+                '<line x1="12" y1="8" x2="12.01" y2="8"/></svg>'
+        };
+        let appDialogResolve = null;
+
+        function openAppDialog(opts) {
+            // A pending dialog is superseded (e.g. an async error arrives while
+            // a confirm is open): resolve it as cancelled so no caller hangs.
+            if (appDialogResolve) {
+                const previous = appDialogResolve;
+                appDialogResolve = null;
+                previous(false);
+            }
+            const danger = opts.danger !== false;
+            const content = document.getElementById('app-dialog-content');
+            const icon = document.getElementById('app-dialog-icon');
+            const cancel = document.getElementById('app-dialog-cancel');
+            const ok = document.getElementById('app-dialog-ok');
+            content.className = 'confirm-modal-content' + (danger ? '' : ' info');
+            icon.className = 'confirm-modal-icon' + (danger ? '' : ' info');
+            icon.innerHTML = danger ? APP_DIALOG_ICONS.danger : APP_DIALOG_ICONS.info;
+            document.getElementById('app-dialog-title').textContent =
+                opts.title || (danger ? 'Confirm' : 'Notice');
+            // textContent: server/device/user supplied strings must never be
+            // interpreted as markup.
+            document.getElementById('app-dialog-message').textContent = opts.message || '';
+            cancel.style.display = opts.cancelText ? '' : 'none';
+            cancel.textContent = opts.cancelText || 'Cancel';
+            ok.className = danger ? 'danger-btn' : 'primary-btn';
+            ok.textContent = opts.okText || 'OK';
+            document.getElementById('app-dialog').classList.add('active');
+            setTimeout(() => ok.focus(), 0);
+            return new Promise(resolve => { appDialogResolve = resolve; });
+        }
+
+        function closeAppDialog(result) {
+            document.getElementById('app-dialog').classList.remove('active');
+            const resolve = appDialogResolve;
+            appDialogResolve = null;
+            if (resolve) resolve(!!result);
+        }
+
+        // Fire-and-forget replacement for alert().
+        function appAlert(message, title) {
+            return openAppDialog({ title: title || 'Notice', message, okText: 'OK', danger: false });
+        }
+
+        // Promise<boolean> replacement for confirm().
+        function appConfirm(message, opts) {
+            opts = opts || {};
+            return openAppDialog({
+                title: opts.title || 'Confirm',
+                message,
+                okText: opts.okText || 'OK',
+                cancelText: opts.cancelText || 'Cancel',
+                danger: opts.danger !== false
+            });
+        }
+
         // ===== 删除设备 =====
         // 两种情况都删除服务端 devices.json 中的历史记录；在线设备额外按 MFC
         // 的做法发送单字节 TOKEN_UNINSTALL（卸载主机）。都先弹二次确认。
@@ -4463,7 +4562,7 @@
         function askDeleteDevice(id) {
             if (!canDeleteDevices()) return;
             const d = devices.find(x => String(x.id) === String(id));
-            if (!d) { alert('Device not found'); return; }
+            if (!d) { appAlert('Device not found.', 'Device Not Found'); return; }
             const offline = d.online === false;
             const name = displayName(d);
             pendingDeleteDeviceId = String(id);
@@ -4559,8 +4658,10 @@
             }
         }
 
-        function deleteUser(username) {
-            if (!confirm('Delete user "' + username + '"?')) return;
+        async function deleteUser(username) {
+            const ok = await appConfirm('Delete user "' + username + '"?',
+                { title: 'Delete User', okText: 'Delete' });
+            if (!ok) return;
             if (ws && ws.readyState === WebSocket.OPEN && token) {
                 ws.send(JSON.stringify({ cmd: 'delete_user', token, username }));
             }
@@ -4792,7 +4893,7 @@
         function connectDevice(id, fromWall) {
             const dev = devices.find(d => d.id === id || d.id === String(id));
             if (!dev || !dev.online) {
-                alert('Device is offline');
+                appAlert('Device is offline.', 'Device Offline');
                 return;
             }
             // 无显示器（screen 字段格式 "n:WxH"，n=0 表示无显示器）→ 远程桌面没有意义，
@@ -4804,7 +4905,7 @@
                 return;
             }
             const compat = checkWebCodecs();
-            if (!compat.supported) { alert('Browser does not support H264: ' + compat.reason); return; }
+            if (!compat.supported) { appAlert('Browser does not support H264: ' + compat.reason, 'H.264 Not Supported'); return; }
             const sid = String(id);
             // 同页直接切设备（正常 UI 不会发生）：先释放旧 focus 引用。
             if (currentDevice && String(currentDevice.id) !== sid) {
@@ -4842,11 +4943,11 @@
 
         function openTerminal(id) {
             if (typeof Terminal === 'undefined') {
-                alert('Terminal library not loaded yet, please retry');
+                appAlert('Terminal library not loaded yet, please retry.', 'Terminal Unavailable');
                 return;
             }
             const dev = devices.find(d => d.id === id || d.id === String(id));
-            if (!dev || !dev.online) { alert('Device is offline'); return; }
+            if (!dev || !dev.online) { appAlert('Device is offline.', 'Device Offline'); return; }
             // 已经有终端在跑：直接 show（重连同设备视为重置）
             if (termState.deviceId && termState.deviceId !== String(id)) {
                 closeTerminal();
@@ -6392,6 +6493,8 @@
         // Desktop keyboard handling
         document.addEventListener('keydown', function(e) {
             if (!document.getElementById('screen-page').classList.contains('active')) return;
+            // Keys belong to an open in-app dialog (buttons are not INPUT/TEXTAREA).
+            if (document.getElementById('app-dialog').classList.contains('active')) return;
             if (e.target.tagName === 'INPUT' || e.target.tagName === 'TEXTAREA') return;
             // F11 belongs to the local fullscreen toggle UNLESS we're actively
             // controlling the remote — see the F11 handler above. Skip here