diff --git a/frontends/ui/src/adapters/ui/icons.tsx b/frontends/ui/src/adapters/ui/icons.tsx
index 14db1d57..54c48d49 100644
--- a/frontends/ui/src/adapters/ui/icons.tsx
+++ b/frontends/ui/src/adapters/ui/icons.tsx
@@ -111,6 +111,7 @@ export const Copy = createIcon('copy-generic')
 export const Download = createIcon('download')
 export const Upload = createIcon('upload')
 export const Share = createIcon('share')
+export const OpenExternal = createIcon('open-external')
 export const Refresh = createIcon('refresh')
 
 // ---------------------------------------------------------------------------
diff --git a/frontends/ui/src/features/layout/components/AppBar.spec.tsx b/frontends/ui/src/features/layout/components/AppBar.spec.tsx
index 536cf45a..017d6bbb 100644
--- a/frontends/ui/src/features/layout/components/AppBar.spec.tsx
+++ b/frontends/ui/src/features/layout/components/AppBar.spec.tsx
@@ -10,6 +10,7 @@ import { AppBar } from './AppBar'
 const mockToggleSessionsPanel = vi.fn()
 const mockOpenRightPanel = vi.fn()
 const mockCloseRightPanel = vi.fn()
+const mockSetTheme = vi.fn()
 
 vi.mock('../store', () => ({
   useLayoutStore: () => ({
@@ -17,6 +18,8 @@ vi.mock('../store', () => ({
     rightPanel: null,
     openRightPanel: mockOpenRightPanel,
     closeRightPanel: mockCloseRightPanel,
+    theme: 'system',
+    setTheme: mockSetTheme,
   }),
 }))
 
@@ -66,7 +69,7 @@ describe('AppBar', () => {
     expect(screen.getByRole('button', { name: /create new session/i })).toBeDisabled()
     expect(screen.getByRole('button', { name: /toggle sessions sidebar/i })).toBeDisabled()
     expect(screen.getByRole('button', { name: /add data sources/i })).toBeDisabled()
-    expect(screen.getByRole('button', { name: /open settings/i })).toBeDisabled()
+    expect(screen.getByRole('button', { name: /open documentation/i })).not.toBeDisabled()
   })
 
   test('enables action buttons when authenticated', () => {
@@ -75,7 +78,7 @@ describe('AppBar', () => {
     expect(screen.getByRole('button', { name: /create new session/i })).not.toBeDisabled()
     expect(screen.getByRole('button', { name: /toggle sessions sidebar/i })).not.toBeDisabled()
     expect(screen.getByRole('button', { name: /add data sources/i })).not.toBeDisabled()
-    expect(screen.getByRole('button', { name: /open settings/i })).not.toBeDisabled()
+    expect(screen.getByRole('button', { name: /open documentation/i })).not.toBeDisabled()
   })
 
   test('calls onNewSession when logo button clicked', async () => {
@@ -117,16 +120,6 @@ describe('AppBar', () => {
     expect(mockOpenRightPanel).toHaveBeenCalledWith('data-sources')
   })
 
-  test('opens settings panel when Settings clicked', async () => {
-    const user = userEvent.setup()
-
-    render(<AppBar isAuthenticated={true} />)
-
-    await user.click(screen.getByRole('button', { name: /open settings/i }))
-
-    expect(mockOpenRightPanel).toHaveBeenCalledWith('settings')
-  })
-
   test('renders Docs button that opens in new tab', () => {
     render(<AppBar />)
 
@@ -168,8 +161,9 @@ describe('AppBar', () => {
       })
       await user.click(avatarButton)
 
-      // Popover should show "Default User" and info message
+      // Popover should show "Default User", theme control, and info message
       expect(screen.getByText('Default User')).toBeInTheDocument()
+      expect(screen.getByRole('radiogroup', { name: /theme/i })).toBeInTheDocument()
       expect(screen.getByText('Authentication Not Configured')).toBeInTheDocument()
     })
 
@@ -193,7 +187,7 @@ describe('AppBar', () => {
       expect(screen.getByRole('button', { name: /create new session/i })).not.toBeDisabled()
       expect(screen.getByRole('button', { name: /toggle sessions sidebar/i })).not.toBeDisabled()
       expect(screen.getByRole('button', { name: /add data sources/i })).not.toBeDisabled()
-      expect(screen.getByRole('button', { name: /open settings/i })).not.toBeDisabled()
+      expect(screen.getByRole('button', { name: /open documentation/i })).not.toBeDisabled()
     })
 
     test('shows session title when auth is disabled', () => {
diff --git a/frontends/ui/src/features/layout/components/AppBar.tsx b/frontends/ui/src/features/layout/components/AppBar.tsx
index 6919c343..d11124df 100644
--- a/frontends/ui/src/features/layout/components/AppBar.tsx
+++ b/frontends/ui/src/features/layout/components/AppBar.tsx
@@ -5,7 +5,7 @@
  * AppBar Component
  *
  * Top navigation bar with menu toggle, logo, session title,
- * and action buttons (Add Sources, Settings, Docs, User Avatar).
+ * and action buttons (Add Sources, Docs, User Avatar).
  *
  * Shows different states based on authentication:
  * - Auth disabled: Default User avatar with info tooltip (no sign in/out)
@@ -15,10 +15,11 @@
 
 'use client'
 
-import { type FC, useCallback, useState } from 'react'
+import { type CSSProperties, type FC, useCallback, useState } from 'react'
 import { Flex, Text, Button, Logo, Avatar, Popover, Divider } from '@/adapters/ui'
-import { Menu, Globe, Settings, Book, Lock, Logout, ChevronRight, Info } from '@/adapters/ui/icons'
+import { Menu, Globe, Book, Lock, Logout, OpenExternal, Info, Moon, Sun } from '@/adapters/ui/icons'
 import { useLayoutStore } from '../store'
+import type { ThemeMode } from '../types'
 
 interface AppBarProps {
   /** Current session title to display */
@@ -43,6 +44,17 @@ interface AppBarProps {
   onSignOut?: () => void
 }
 
+/** Transparent popover shell with outline only (no KUI fill/shadow). */
+const USER_MENU_POPOVER_CLASS =
+  '!bg-transparent !p-0 !shadow-none rounded-[var(--radius-md)] border border-base text-primary'
+
+const USER_MENU_POPOVER_STYLE: CSSProperties = {
+  backgroundColor: 'transparent',
+  boxShadow: 'none',
+  padding: 0,
+  marginTop: 4,
+}
+
 /**
  * Main navigation bar at the top of the application.
  * Controls sidebar toggles and navigation actions.
@@ -74,15 +86,6 @@ export const AppBar: FC<AppBarProps> = ({
     }
   }, [rightPanel, openRightPanel, closeRightPanel, isAuthenticated])
 
-  const handleSettingsClick = useCallback(() => {
-    if (!isAuthenticated) return
-    if (rightPanel === 'settings') {
-      closeRightPanel()
-    } else {
-      openRightPanel('settings')
-    }
-  }, [rightPanel, openRightPanel, closeRightPanel, isAuthenticated])
-
   const handleDocsClick = useCallback(() => {
     window.open('https://github.com/NVIDIA-AI-Blueprints/aiq', '_blank')
   }, [])
@@ -164,21 +167,6 @@ export const AppBar: FC<AppBarProps> = ({
               <Text kind="label/regular/md">Data Sources</Text>
             </Flex>
           </Button>
-
-          <Button
-            kind="tertiary"
-            size="small"
-            onClick={handleSettingsClick}
-            disabled={!isAuthenticated}
-            aria-label="Open settings"
-            title="Open settings"
-          >
-            <Flex align="center" gap="1">
-              <Settings className="h-4 w-4" />
-              <Text kind="label/regular/md">Settings</Text>
-            </Flex>
-          </Button>
-
           <Button
             kind="tertiary"
             size="small"
@@ -188,8 +176,8 @@ export const AppBar: FC<AppBarProps> = ({
           >
             <Flex align="center" gap="1">
               <Book className="h-4 w-4" />
-              <Text kind="label/regular/md">Docs</Text>
-              <ChevronRight className="h-3 w-3 -rotate-45" />
+              <Text kind="label/regular/md">Documentation</Text>
+              <OpenExternal className="h-4 w-4" />
             </Flex>
           </Button>
 
@@ -200,6 +188,8 @@ export const AppBar: FC<AppBarProps> = ({
               onOpenChange={setIsUserMenuOpen}
               side="bottom"
               align="end"
+              className={USER_MENU_POPOVER_CLASS}
+              style={USER_MENU_POPOVER_STYLE}
               slotContent={<AuthDisabledContent />}
             >
               <Button
@@ -218,6 +208,8 @@ export const AppBar: FC<AppBarProps> = ({
               onOpenChange={setIsUserMenuOpen}
               side="bottom"
               align="end"
+              className={USER_MENU_POPOVER_CLASS}
+              style={USER_MENU_POPOVER_STYLE}
               slotContent={<UserDropdownContent user={user} onSignOut={handleSignOut} />}
             >
               <Button
@@ -267,6 +259,77 @@ interface UserDropdownContentProps {
   onSignOut?: () => void
 }
 
+const APPEARANCE_SEGMENTS: { mode: ThemeMode; label: string }[] = [
+  { mode: 'system', label: 'System' },
+  { mode: 'dark', label: 'Dark' },
+  { mode: 'light', label: 'Light' },
+]
+
+const AppearanceThemeControl: FC = () => {
+  const { theme, setTheme } = useLayoutStore()
+
+  return (
+    <Flex direction="col" gap="2">
+      <Text kind="label/regular/sm" className="text-subtle">
+        Appearance
+      </Text>
+      <Flex
+        align="center"
+        gap="1"
+        className="p-1"
+        role="radiogroup"
+        aria-label="Theme"
+        style={{
+          background: 'var(--color-component-track-background, #FFFFFF33)',
+          borderRadius: 'var(--radius-lg)',
+        }}
+      >
+        {APPEARANCE_SEGMENTS.map(({ mode, label }) => {
+          const selected = theme === mode
+          return (
+            <Button
+              key={mode}
+              type="button"
+              role="radio"
+              aria-checked={selected}
+              aria-label={`${label} theme`}
+              kind="tertiary"
+              size="small"
+              onClick={() => setTheme(mode)}
+              className={`h-auto min-h-9 flex-1 rounded-[var(--radius-md)] border-0 px-2 py-1.5 shadow-none transition-colors focus-visible:ring-2 focus-visible:ring-[var(--color-border-focus,#76b900)] ${
+                selected ? '!bg-black !text-white hover:!bg-black' : 'bg-transparent hover:bg-white/10'
+              }`}
+            >
+              <Flex align="center" justify="center" gap="1" className="w-full">
+                {mode === 'dark' ? (
+                  <Moon
+                    className={`h-4 w-4 shrink-0 ${selected ? '!text-white' : 'text-primary'}`}
+                    width={16}
+                    height={16}
+                  />
+                ) : null}
+                {mode === 'light' ? (
+                  <Sun
+                    className={`h-4 w-4 shrink-0 ${selected ? '!text-white' : 'text-primary'}`}
+                    width={16}
+                    height={16}
+                  />
+                ) : null}
+                <Text
+                  kind={selected ? 'label/semibold/sm' : 'label/regular/sm'}
+                  className={selected ? 'text-white' : 'text-primary'}
+                >
+                  {label}
+                </Text>
+              </Flex>
+            </Button>
+          )
+        })}
+      </Flex>
+    </Flex>
+  )
+}
+
 const UserDropdownContent: FC<UserDropdownContentProps> = ({ user, onSignOut }) => {
   return (
     <Flex direction="col" gap="3" className="min-w-[240px] p-4">
@@ -291,6 +354,7 @@ const UserDropdownContent: FC<UserDropdownContentProps> = ({ user, onSignOut })
 
       <Divider />
 
+      <AppearanceThemeControl />
       {/* Sign out button */}
       <Button
         kind="secondary"
@@ -328,8 +392,10 @@ const AuthDisabledContent: FC = () => {
 
       <Divider />
 
+      <AppearanceThemeControl />
+
       {/* Info message */}
-      <Flex align="center" gap="2" className="rounded bg-[var(--background-color-surface-raised)] p-3">
+      <Flex align="center" gap="2" className="rounded border border-base p-3">
         <Info className="h-4 w-4 shrink-0 text-[var(--text-color-subtle)]" />
         <Text kind="body/regular/sm" className="text-subtle">
           Authentication Not Configured
diff --git a/frontends/ui/src/features/layout/components/MainLayout.spec.tsx b/frontends/ui/src/features/layout/components/MainLayout.spec.tsx
index 2e7d903e..e284bf77 100644
--- a/frontends/ui/src/features/layout/components/MainLayout.spec.tsx
+++ b/frontends/ui/src/features/layout/components/MainLayout.spec.tsx
@@ -98,10 +98,6 @@ vi.mock('./DataSourcesPanel', () => ({
   DataSourcesPanel: () => <div data-testid="data-sources-panel">Data Sources Panel</div>,
 }))
 
-vi.mock('./SettingsPanel', () => ({
-  SettingsPanel: () => <div data-testid="settings-panel">Settings Panel</div>,
-}))
-
 import { useChatStore } from '@/features/chat'
 import { useLayoutStore } from '../store'
 
@@ -119,7 +115,6 @@ describe('MainLayout', () => {
     expect(screen.getByTestId('input-area')).toBeInTheDocument()
     expect(screen.getByTestId('research-panel')).toBeInTheDocument()
     expect(screen.getByTestId('data-sources-panel')).toBeInTheDocument()
-    expect(screen.getByTestId('settings-panel')).toBeInTheDocument()
   })
 
   test('passes session title to AppBar', () => {
diff --git a/frontends/ui/src/features/layout/components/MainLayout.tsx b/frontends/ui/src/features/layout/components/MainLayout.tsx
index 233853bc..be1efebf 100644
--- a/frontends/ui/src/features/layout/components/MainLayout.tsx
+++ b/frontends/ui/src/features/layout/components/MainLayout.tsx
@@ -9,7 +9,7 @@
  * - SessionsPanel (left, overlay)
  * - ChatArea + InputArea (center, responsive width)
  * - ResearchPanel (right, pushes content - takes 60% when open)
- * - DataSourcesPanel / SettingsPanel (right, overlay)
+ * - DataSourcesPanel (right, overlay)
  *
  * Handles auth state to show different UI for logged-in vs logged-out users.
  */
@@ -25,7 +25,6 @@ import { ChatArea } from './ChatArea'
 import { InputArea } from './InputArea'
 import { ResearchPanel } from './ResearchPanel'
 import { DataSourcesPanel } from './DataSourcesPanel'
-import { SettingsPanel } from './SettingsPanel'
 import { useChatStore, useDeepResearch, NoSourcesBanner } from '@/features/chat'
 import { hasActiveDeepResearchJob } from '@/features/chat/lib/session-activity'
 import { useLayoutStore } from '../store'
@@ -193,9 +192,6 @@ export const MainLayout: FC<MainLayoutProps> = ({
 
       {/* Data Sources Panel (Right) - Overlay */}
       <DataSourcesPanel />
-
-      {/* Settings Panel (Right) - Overlay */}
-      <SettingsPanel />
     </Flex>
   )
 }