diff --git a/src-tauri/src/types.rs b/src-tauri/src/types.rs
index ce33c3f13..612c0faff 100644
--- a/src-tauri/src/types.rs
+++ b/src-tauri/src/types.rs
@@ -260,6 +260,8 @@ pub(crate) struct AppSettings {
     pub(crate) last_composer_reasoning_effort: Option<String>,
     #[serde(default = "default_ui_scale", rename = "uiScale")]
     pub(crate) ui_scale: f64,
+    #[serde(default = "default_theme", rename = "theme")]
+    pub(crate) theme: String,
     #[serde(
         default = "default_notification_sounds_enabled",
         rename = "notificationSoundsEnabled"
@@ -323,6 +325,10 @@ fn default_ui_scale() -> f64 {
     1.0
 }
 
+fn default_theme() -> String {
+    "system".to_string()
+}
+
 fn default_composer_model_shortcut() -> Option<String> {
     Some("cmd+shift+m".to_string())
 }
@@ -381,6 +387,7 @@ impl Default for AppSettings {
             last_composer_model_id: None,
             last_composer_reasoning_effort: None,
             ui_scale: 1.0,
+            theme: default_theme(),
             notification_sounds_enabled: true,
             experimental_collab_enabled: false,
             experimental_steer_enabled: false,
@@ -421,6 +428,7 @@ mod tests {
         assert!(settings.last_composer_model_id.is_none());
         assert!(settings.last_composer_reasoning_effort.is_none());
         assert!((settings.ui_scale - 1.0).abs() < f64::EPSILON);
+        assert_eq!(settings.theme, "system");
         assert!(settings.notification_sounds_enabled);
         assert!(!settings.experimental_steer_enabled);
         assert!(!settings.dictation_enabled);
diff --git a/src/App.tsx b/src/App.tsx
index f27e476bb..4eda5281d 100644
--- a/src/App.tsx
+++ b/src/App.tsx
@@ -1149,7 +1149,34 @@ function MainApp() {
     onDebug: addDebugEntry,
   });
   const isDefaultScale = Math.abs(uiScale - 1) < 0.001;
-  const appClassName = `app ${isCompact ? "layout-compact" : "layout-desktop"}${
+  const [systemTheme, setSystemTheme] = useState<"dark" | "light">(() => {
+    if (typeof window === "undefined" || !window.matchMedia) {
+      return "dark";
+    }
+    return window.matchMedia("(prefers-color-scheme: dark)").matches ? "dark" : "light";
+  });
+  useEffect(() => {
+    if (typeof window === "undefined" || !window.matchMedia) {
+      return;
+    }
+    const media = window.matchMedia("(prefers-color-scheme: dark)");
+    const handleChange = (event: MediaQueryListEvent) => {
+      setSystemTheme(event.matches ? "dark" : "light");
+    };
+    setSystemTheme(media.matches ? "dark" : "light");
+    if (media.addEventListener) {
+      media.addEventListener("change", handleChange);
+      return () => media.removeEventListener("change", handleChange);
+    }
+    media.addListener(handleChange);
+    return () => media.removeListener(handleChange);
+  }, []);
+  const resolvedTheme =
+    appSettings.theme === "system" ? systemTheme : appSettings.theme;
+  const themeClassName = resolvedTheme === "light" ? "theme-light" : "theme-dark";
+  const appClassName = `app ${themeClassName} ${
+    isCompact ? "layout-compact" : "layout-desktop"
+  }${
     isPhone ? " layout-phone" : ""
   }${isTablet ? " layout-tablet" : ""}${
     reduceTransparency ? " reduced-transparency" : ""
@@ -1193,6 +1220,7 @@ function MainApp() {
     activeRateLimits,
     approvals,
     handleApprovalDecision,
+    themePreference: resolvedTheme,
     onOpenSettings: () => handleOpenSettings(),
     onOpenDictationSettings: () => handleOpenSettings("dictation"),
     onOpenDebug: handleDebugClick,
diff --git a/src/features/git/components/GitDiffViewer.tsx b/src/features/git/components/GitDiffViewer.tsx
index 5f51eadfe..dfa2b99c0 100644
--- a/src/features/git/components/GitDiffViewer.tsx
+++ b/src/features/git/components/GitDiffViewer.tsx
@@ -20,6 +20,7 @@ type GitDiffViewerProps = {
   scrollRequestId?: number;
   isLoading: boolean;
   error: string | null;
+  themePreference?: "system" | "dark" | "light";
   pullRequest?: GitHubPullRequest | null;
   pullRequestComments?: GitHubPullRequestComment[];
   pullRequestCommentsLoading?: boolean;
@@ -119,6 +120,7 @@ export function GitDiffViewer({
   scrollRequestId,
   isLoading,
   error,
+  themePreference = "system",
   pullRequest,
   pullRequestComments,
   pullRequestCommentsLoading = false,
@@ -131,10 +133,15 @@ export function GitDiffViewer({
   const ignoreActivePathUntilRef = useRef<number>(0);
   const lastScrollRequestIdRef = useRef<number | null>(null);
   const poolOptions = useMemo(() => ({ workerFactory }), []);
-  const highlighterOptions = useMemo(
-    () => ({ theme: { dark: "pierre-dark", light: "pierre-light" } }),
-    [],
-  );
+  const highlighterOptions = useMemo(() => {
+    if (themePreference === "dark") {
+      return { theme: "pierre-dark" };
+    }
+    if (themePreference === "light") {
+      return { theme: "pierre-light" };
+    }
+    return { theme: { dark: "pierre-dark", light: "pierre-light" } };
+  }, [themePreference]);
   const indexByPath = useMemo(() => {
     const map = new Map<string, number>();
     diffs.forEach((entry, index) => {
diff --git a/src/features/layout/hooks/useLayoutNodes.tsx b/src/features/layout/hooks/useLayoutNodes.tsx
index 3a4314047..0994c93ef 100644
--- a/src/features/layout/hooks/useLayoutNodes.tsx
+++ b/src/features/layout/hooks/useLayoutNodes.tsx
@@ -207,6 +207,7 @@ type LayoutNodesOptions = {
   gitDiffs: GitDiffViewerItem[];
   gitDiffLoading: boolean;
   gitDiffError: string | null;
+  themePreference?: "system" | "dark" | "light";
   onDiffActivePathChange?: (path: string) => void;
   onSendPrompt: (text: string) => void | Promise<void>;
   onSendPromptToNewAgent: (text: string) => void | Promise<void>;
@@ -597,6 +598,7 @@ export function useLayoutNodes(options: LayoutNodesOptions): LayoutNodesResult {
       scrollRequestId={options.diffScrollRequestId}
       isLoading={options.gitDiffLoading}
       error={options.gitDiffError}
+      themePreference={options.themePreference}
       pullRequest={options.selectedPullRequest}
       pullRequestComments={options.selectedPullRequestComments}
       pullRequestCommentsLoading={options.selectedPullRequestCommentsLoading}
diff --git a/src/features/settings/components/SettingsView.tsx b/src/features/settings/components/SettingsView.tsx
index b6b44aa6e..4edf9cad4 100644
--- a/src/features/settings/components/SettingsView.tsx
+++ b/src/features/settings/components/SettingsView.tsx
@@ -706,6 +706,30 @@ export function SettingsView({
                     </button>
                   </div>
                 </div>
+                <div className="settings-toggle-row">
+                  <div>
+                    <div className="settings-toggle-title">Theme</div>
+                    <div className="settings-toggle-subtitle">
+                      Follow macOS appearance or force a light/dark theme.
+                    </div>
+                  </div>
+                  <select
+                    id="theme-preference"
+                    className="settings-select settings-select--theme"
+                    value={appSettings.theme}
+                    onChange={(event) =>
+                      void onUpdateAppSettings({
+                        ...appSettings,
+                        theme: event.target.value as AppSettings["theme"],
+                      })
+                    }
+                    aria-label="Theme"
+                  >
+                    <option value="system">System</option>
+                    <option value="dark">Dark</option>
+                    <option value="light">Light</option>
+                  </select>
+                </div>
                 <div className="settings-subsection-title">Sounds</div>
                 <div className="settings-subsection-subtitle">
                   Control notification audio alerts.
diff --git a/src/features/settings/hooks/useAppSettings.ts b/src/features/settings/hooks/useAppSettings.ts
index 85a48882c..2c528cbd0 100644
--- a/src/features/settings/hooks/useAppSettings.ts
+++ b/src/features/settings/hooks/useAppSettings.ts
@@ -15,6 +15,7 @@ const defaultSettings: AppSettings = {
   lastComposerModelId: null,
   lastComposerReasoningEffort: null,
   uiScale: UI_SCALE_DEFAULT,
+  theme: "system",
   notificationSoundsEnabled: true,
   experimentalCollabEnabled: false,
   experimentalSteerEnabled: false,
@@ -27,9 +28,16 @@ const defaultSettings: AppSettings = {
 };
 
 function normalizeAppSettings(settings: AppSettings): AppSettings {
+  const theme =
+    settings.theme === "light" ||
+    settings.theme === "dark" ||
+    settings.theme === "system"
+      ? settings.theme
+      : "system";
   return {
     ...settings,
     uiScale: clampUiScale(settings.uiScale),
+    theme,
   };
 }
 
diff --git a/src/styles/base.css b/src/styles/base.css
index 13f12b09a..f2745b670 100644
--- a/src/styles/base.css
+++ b/src/styles/base.css
@@ -70,6 +70,14 @@
   --ui-scale: 1;
 }
 
+.app.theme-light {
+  color-scheme: light;
+}
+
+.app.theme-dark {
+  color-scheme: dark;
+}
+
 .app.reduced-transparency {
   --surface-sidebar: rgba(18, 18, 18, 0.92);
   --surface-topbar: rgba(10, 14, 20, 0.94);
@@ -95,36 +103,35 @@
   --surface-popover: rgba(16, 20, 30, 0.995);
 }
 
-  @media (prefers-color-scheme: light) {
-  :root {
-    --text-primary: #1a1d24;
-    --text-strong: #0e1118;
-    --text-emphasis: rgba(17, 20, 28, 0.9);
-    --text-stronger: rgba(17, 20, 28, 0.85);
-    --text-quiet: rgba(17, 20, 28, 0.75);
-    --text-muted: rgba(17, 20, 28, 0.7);
-    --text-subtle: rgba(17, 20, 28, 0.6);
-    --text-faint: rgba(17, 20, 28, 0.5);
-    --text-fainter: rgba(17, 20, 28, 0.45);
-    --text-dim: rgba(17, 20, 28, 0.35);
-    --surface-sidebar: rgba(246, 247, 250, 0.82);
-    --surface-topbar: rgba(250, 251, 253, 0.9);
-    --surface-right-panel: rgba(245, 247, 250, 0.82);
-    --surface-composer: rgba(250, 251, 253, 0.9);
-    --surface-messages: rgba(238, 241, 246, 0.9);
-    --surface-card: rgba(255, 255, 255, 0.72);
-    --surface-card-strong: rgba(255, 255, 255, 0.92);
-    --surface-card-muted: rgba(255, 255, 255, 0.7);
-    --surface-item: rgba(255, 255, 255, 0.6);
-    --surface-control: rgba(15, 23, 36, 0.08);
-    --surface-control-hover: rgba(15, 23, 36, 0.12);
+.app.theme-light {
+  --text-primary: #1a1d24;
+  --text-strong: #0e1118;
+  --text-emphasis: rgba(17, 20, 28, 0.9);
+  --text-stronger: rgba(17, 20, 28, 0.85);
+  --text-quiet: rgba(17, 20, 28, 0.75);
+  --text-muted: rgba(17, 20, 28, 0.7);
+  --text-subtle: rgba(17, 20, 28, 0.6);
+  --text-faint: rgba(17, 20, 28, 0.5);
+  --text-fainter: rgba(17, 20, 28, 0.45);
+  --text-dim: rgba(17, 20, 28, 0.35);
+  --surface-sidebar: rgba(246, 247, 250, 0.82);
+  --surface-topbar: rgba(250, 251, 253, 0.9);
+  --surface-right-panel: rgba(245, 247, 250, 0.82);
+  --surface-composer: rgba(250, 251, 253, 0.9);
+  --surface-messages: rgba(238, 241, 246, 0.9);
+  --surface-card: rgba(255, 255, 255, 0.72);
+  --surface-card-strong: rgba(255, 255, 255, 0.92);
+  --surface-card-muted: rgba(255, 255, 255, 0.7);
+  --surface-item: rgba(255, 255, 255, 0.6);
+  --surface-control: rgba(15, 23, 36, 0.08);
+  --surface-control-hover: rgba(15, 23, 36, 0.12);
   --surface-control-disabled: rgba(15, 23, 36, 0.05);
   --surface-hover: rgba(15, 23, 36, 0.06);
   --surface-active: rgba(77, 153, 255, 0.18);
-    --surface-approval: rgba(246, 248, 252, 0.92);
-    --surface-debug: rgba(242, 244, 248, 0.9);
-    --surface-command: rgba(245, 247, 250, 0.95);
-    --surface-diff-card: rgba(240, 243, 248, 0.92);
+  --surface-approval: rgba(246, 248, 252, 0.92);
+  --surface-debug: rgba(242, 244, 248, 0.9);
+  --surface-command: rgba(245, 247, 250, 0.95);
+  --surface-diff-card: rgba(240, 243, 248, 0.92);
   --surface-bubble: rgba(255, 255, 255, 0.9);
   --surface-bubble-user: rgba(77, 153, 255, 0.22);
   --surface-context-core: rgba(255, 255, 255, 0.9);
@@ -135,46 +142,45 @@
   --text-review-active: rgba(120, 30, 70, 0.9);
   --surface-review-done: rgba(140, 235, 200, 0.35);
   --text-review-done: rgba(20, 90, 60, 0.9);
-    --border-subtle: rgba(15, 23, 36, 0.08);
-    --border-muted: rgba(15, 23, 36, 0.06);
-    --border-strong: rgba(15, 23, 36, 0.14);
-    --border-stronger: rgba(15, 23, 36, 0.18);
-    --border-quiet: rgba(15, 23, 36, 0.2);
-    --border-accent: rgba(77, 153, 255, 0.5);
-    --border-accent-soft: rgba(77, 153, 255, 0.28);
+  --border-subtle: rgba(15, 23, 36, 0.08);
+  --border-muted: rgba(15, 23, 36, 0.06);
+  --border-strong: rgba(15, 23, 36, 0.14);
+  --border-stronger: rgba(15, 23, 36, 0.18);
+  --border-quiet: rgba(15, 23, 36, 0.2);
+  --border-accent: rgba(77, 153, 255, 0.5);
+  --border-accent-soft: rgba(77, 153, 255, 0.28);
   --text-accent: rgba(45, 93, 170, 0.7);
   --shadow-accent: rgba(90, 140, 210, 0.18);
   --status-success: rgba(30, 155, 110, 0.9);
-    --status-warning: rgba(215, 120, 20, 0.9);
-    --status-error: rgba(200, 45, 45, 0.9);
-    --status-unknown: rgba(17, 20, 28, 0.25);
+  --status-warning: rgba(215, 120, 20, 0.9);
+  --status-error: rgba(200, 45, 45, 0.9);
+  --status-unknown: rgba(17, 20, 28, 0.25);
   --select-caret: rgba(15, 23, 36, 0.45);
-  }
+}
 
-  .app.reduced-transparency {
-    --surface-sidebar: rgba(240, 242, 247, 0.98);
-    --surface-topbar: rgba(244, 246, 250, 0.98);
-    --surface-right-panel: rgba(242, 244, 248, 0.98);
-    --surface-composer: rgba(244, 246, 250, 0.98);
-    --surface-messages: rgba(240, 242, 247, 0.98);
-    --surface-card: rgba(255, 255, 255, 0.96);
-    --surface-card-strong: rgba(255, 255, 255, 0.98);
-    --surface-card-muted: rgba(252, 253, 255, 0.96);
-    --surface-item: rgba(250, 251, 253, 0.96);
-    --surface-control: rgba(15, 23, 36, 0.12);
-    --surface-control-hover: rgba(15, 23, 36, 0.18);
-    --surface-control-disabled: rgba(15, 23, 36, 0.08);
-    --surface-hover: rgba(15, 23, 36, 0.1);
-    --surface-active: rgba(77, 153, 255, 0.22);
-    --surface-approval: rgba(248, 249, 252, 0.98);
-    --surface-debug: rgba(246, 248, 252, 0.98);
-    --surface-command: rgba(250, 251, 253, 0.98);
-    --surface-diff-card: rgba(244, 246, 250, 0.98);
-    --surface-bubble: rgba(255, 255, 255, 0.98);
-    --surface-bubble-user: rgba(77, 153, 255, 0.28);
-    --surface-context-core: rgba(255, 255, 255, 0.98);
-    --surface-popover: rgba(255, 255, 255, 0.995);
-  }
+.app.theme-light.reduced-transparency {
+  --surface-sidebar: rgba(240, 242, 247, 0.98);
+  --surface-topbar: rgba(244, 246, 250, 0.98);
+  --surface-right-panel: rgba(242, 244, 248, 0.98);
+  --surface-composer: rgba(244, 246, 250, 0.98);
+  --surface-messages: rgba(240, 242, 247, 0.98);
+  --surface-card: rgba(255, 255, 255, 0.96);
+  --surface-card-strong: rgba(255, 255, 255, 0.98);
+  --surface-card-muted: rgba(252, 253, 255, 0.96);
+  --surface-item: rgba(250, 251, 253, 0.96);
+  --surface-control: rgba(15, 23, 36, 0.12);
+  --surface-control-hover: rgba(15, 23, 36, 0.18);
+  --surface-control-disabled: rgba(15, 23, 36, 0.08);
+  --surface-hover: rgba(15, 23, 36, 0.1);
+  --surface-active: rgba(77, 153, 255, 0.22);
+  --surface-approval: rgba(248, 249, 252, 0.98);
+  --surface-debug: rgba(246, 248, 252, 0.98);
+  --surface-command: rgba(250, 251, 253, 0.98);
+  --surface-diff-card: rgba(244, 246, 250, 0.98);
+  --surface-bubble: rgba(255, 255, 255, 0.98);
+  --surface-bubble-user: rgba(77, 153, 255, 0.28);
+  --surface-context-core: rgba(255, 255, 255, 0.98);
+  --surface-popover: rgba(255, 255, 255, 0.995);
 }
 
 .popover-surface {
@@ -205,6 +211,7 @@ body {
   display: grid;
   grid-template-columns: var(--sidebar-width, 280px) 1fr;
   background: transparent;
+  color: var(--text-primary);
   border-radius: 0;
   overflow: hidden;
   position: relative;
diff --git a/src/styles/composer.css b/src/styles/composer.css
index 3795fa842..5abb09a1e 100644
--- a/src/styles/composer.css
+++ b/src/styles/composer.css
@@ -198,15 +198,13 @@
   position: relative;
 }
 
-@media (prefers-color-scheme: light) {
-  .composer-action {
-    border-color: var(--border-strong);
-    color: var(--text-strong);
-  }
+.app.theme-light .composer-action {
+  border-color: var(--border-strong);
+  color: var(--text-strong);
+}
 
-  .composer-action:hover {
-    color: var(--text-strong);
-  }
+.app.theme-light .composer-action:hover {
+  color: var(--text-strong);
 }
 
 .composer-action--mic.is-active {
diff --git a/src/styles/messages.css b/src/styles/messages.css
index 1da7dd190..d605ac25b 100644
--- a/src/styles/messages.css
+++ b/src/styles/messages.css
@@ -73,11 +73,9 @@
   animation: working-shimmer 2.2s ease-in-out infinite;
 }
 
-@media (prefers-color-scheme: light) {
-  .working-text {
-    color: var(--text-muted);
-    background: none;
-  }
+.app.theme-light .working-text {
+  color: var(--text-muted);
+  background: none;
 }
 
 .turn-complete {
diff --git a/src/styles/settings.css b/src/styles/settings.css
index acd90ad8b..b1991dc86 100644
--- a/src/styles/settings.css
+++ b/src/styles/settings.css
@@ -223,6 +223,10 @@
   font-size: 11px;
 }
 
+.settings-select--theme {
+  min-width: 180px;
+}
+
 .settings-section-title {
   font-size: 15px;
   font-weight: 600;
diff --git a/src/types.ts b/src/types.ts
index 3ad56871c..2e83595fe 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -70,6 +70,7 @@ export type ReviewTarget =
 
 export type AccessMode = "read-only" | "current" | "full-access";
 export type BackendMode = "local" | "remote";
+export type ThemePreference = "system" | "dark" | "light";
 
 export type AppSettings = {
   codexBin: string | null;
@@ -83,6 +84,7 @@ export type AppSettings = {
   lastComposerModelId: string | null;
   lastComposerReasoningEffort: string | null;
   uiScale: number;
+  theme: ThemePreference;
   notificationSoundsEnabled: boolean;
   experimentalCollabEnabled: boolean;
   experimentalSteerEnabled: boolean;