diff --git a/surfsense_local/electron/src/main/index.ts b/surfsense_local/electron/src/main/index.ts
index 1de835749c..df29d0dd5e 100644
--- a/surfsense_local/electron/src/main/index.ts
+++ b/surfsense_local/electron/src/main/index.ts
@@ -1,6 +1,14 @@
 import { join } from "node:path"
 
-import { app, BrowserWindow, ipcMain, Menu, safeStorage, shell } from "electron"
+import {
+  app,
+  BrowserWindow,
+  ipcMain,
+  Menu,
+  nativeTheme,
+  safeStorage,
+  shell,
+} from "electron"
 // Static on purpose: electron-updater is CJS and exposes `autoUpdater` through
 // a getter, which `await import()` cannot see (named export comes back
 // undefined). require() honours it, and the getter is lazy so dev pays nothing.
@@ -32,6 +40,11 @@ import {
   type Updates,
   type UpdateState,
 } from "./updater.ts"
+import {
+  loadThemePreference,
+  saveThemePreference,
+  type ThemePreference,
+} from "./theme-prefs.ts"
 import { loadWindowState, saveWindowState } from "./window-state.ts"
 
 const DEV_RENDERER_URL = "http://localhost:5173"
@@ -185,6 +198,18 @@ function registerDocumentHandlers(dataDir: string): void {
     applyTitleBarOverlay(mainWindow, overlay)
   })
 
+  ipcMain.handle("theme:set", (event, theme: unknown) => {
+    if (
+      !trusted(event.sender) ||
+      event.senderFrame !== event.sender.mainFrame
+    ) {
+      return
+    }
+    if (theme !== "dark" && theme !== "light" && theme !== "system") return
+    saveThemePreference(theme)
+    applyBackgroundColorToAllWindows(theme)
+  })
+
   ipcMain.handle("documents:open", async (event, workspaceId, documentId) => {
     if (
       !trusted(event.sender) ||
@@ -296,6 +321,29 @@ function applyTitleBarOverlay(
   })
 }
 
+// Mirrors --app-shell in frontend/src/index.css (:root / .dark). Used as the
+// BrowserWindow's native backgroundColor so a reload shows the right theme
+// immediately instead of flashing Electron's default opaque white while the
+// page is torn down and reloaded.
+// https://www.electronjs.org/docs/latest/api/browser-window#showing-window-gracefully
+const APP_SHELL_LIGHT = "#f3f2ee"
+const APP_SHELL_DARK = "#101010"
+
+function resolveBackgroundColor(theme: ThemePreference): string {
+  const resolvedDark =
+    theme === "system" ? nativeTheme.shouldUseDarkColors : theme === "dark"
+  return resolvedDark ? APP_SHELL_DARK : APP_SHELL_LIGHT
+}
+
+function currentWindows(): BrowserWindow[] {
+  return BrowserWindow.getAllWindows()
+}
+
+function applyBackgroundColorToAllWindows(theme: ThemePreference): void {
+  const color = resolveBackgroundColor(theme)
+  for (const win of currentWindows()) win.setBackgroundColor(color)
+}
+
 // Packaged only. Dev keeps Electron's default View menu (reload + DevTools).
 // https://www.electronjs.org/docs/latest/tutorial/application-menu
 function installProductionMenu(): void {
@@ -340,6 +388,7 @@ function createWindow(apiUrl: string): void {
   const savedState = app.isPackaged ? loadWindowState() : null
   const win = new BrowserWindow({
     ...(savedState?.bounds ?? { width: 1280, height: 800 }),
+    backgroundColor: resolveBackgroundColor(loadThemePreference()),
     show: false,
     // https://www.electronjs.org/docs/latest/tutorial/custom-title-bar
     titleBarStyle: process.platform === "darwin" ? "hiddenInset" : "hidden",
@@ -398,6 +447,24 @@ function main(): void {
   app.on("web-contents-created", (_event, contents) => {
     denyAppWindows(contents)
   })
+
+  // The renderer's own matchMedia isn't a reliable single source of truth
+  // for the OS theme inside a packaged app (it can lag or diverge from what
+  // Chromium/Electron itself resolves), so nativeTheme is authoritative and
+  // the renderer only ever mirrors it: a sync read on preload boot for the
+  // first paint, then this push on every change.
+  ipcMain.on("theme:get-system", (event) => {
+    event.returnValue = nativeTheme.shouldUseDarkColors ? "dark" : "light"
+  })
+  nativeTheme.on("updated", () => {
+    const systemTheme = nativeTheme.shouldUseDarkColors ? "dark" : "light"
+    for (const win of currentWindows()) {
+      win.webContents.send("theme:system-changed", systemTheme)
+    }
+    if (loadThemePreference() === "system") {
+      applyBackgroundColorToAllWindows("system")
+    }
+  })
   app
     .whenReady()
     .then(async () => {
diff --git a/surfsense_local/electron/src/main/theme-prefs.ts b/surfsense_local/electron/src/main/theme-prefs.ts
new file mode 100644
index 0000000000..b061c15e11
--- /dev/null
+++ b/surfsense_local/electron/src/main/theme-prefs.ts
@@ -0,0 +1,47 @@
+import { readFileSync, renameSync, writeFileSync } from "node:fs"
+import { join } from "node:path"
+
+import { app } from "electron"
+
+// Mirrors the Theme type in frontend/src/components/theme-provider.tsx.
+export type ThemePreference = "dark" | "light" | "system"
+
+const THEME_VALUES: ThemePreference[] = ["dark", "light", "system"]
+
+function prefsPath(): string {
+  return join(app.getPath("userData"), "theme-prefs.json")
+}
+
+function isThemePreference(value: unknown): value is ThemePreference {
+  return (
+    typeof value === "string" && THEME_VALUES.includes(value as ThemePreference)
+  )
+}
+
+export function loadThemePreference(): ThemePreference {
+  try {
+    const parsed: unknown = JSON.parse(readFileSync(prefsPath(), "utf8"))
+    const theme =
+      parsed && typeof parsed === "object"
+        ? (parsed as { theme?: unknown }).theme
+        : undefined
+    return isThemePreference(theme) ? theme : "system"
+  } catch {
+    return "system"
+  }
+}
+
+export function saveThemePreference(theme: ThemePreference): void {
+  try {
+    const path = prefsPath()
+    const temporary = `${path}.tmp`
+    writeFileSync(temporary, JSON.stringify({ theme }))
+    renameSync(temporary, path)
+  } catch (error) {
+    // ponytail: best-effort, same as window-state.ts; a stale/missing pref
+    // just falls back to "system" next launch.
+    process.stderr.write(
+      `[main] failed to save theme preference: ${String(error)}\n`,
+    )
+  }
+}
diff --git a/surfsense_local/electron/src/preload/index.ts b/surfsense_local/electron/src/preload/index.ts
index 5896430913..1b162cfeb8 100644
--- a/surfsense_local/electron/src/preload/index.ts
+++ b/surfsense_local/electron/src/preload/index.ts
@@ -4,6 +4,14 @@ import { contextBridge, ipcRenderer } from "electron"
 const FLAG = "--surfsense-api-url="
 const arg = process.argv.find((a) => a.startsWith(FLAG))
 
+// nativeTheme (main process) is the single source of truth for the OS theme.
+// A sync IPC read here means the value is already correct by the time the
+// page's own first-paint script runs, and the "updated" push keeps it live.
+let systemTheme = ipcRenderer.sendSync("theme:get-system") as "dark" | "light"
+ipcRenderer.on("theme:system-changed", (_event, theme: unknown) => {
+  if (theme === "dark" || theme === "light") systemTheme = theme
+})
+
 // the renderer talks HTTP to this base and never sees Node or the sidecars
 contextBridge.exposeInMainWorld("surfsense", {
   apiUrl: arg ? arg.slice(FLAG.length) : "http://127.0.0.1:8000",
@@ -31,4 +39,18 @@ contextBridge.exposeInMainWorld("surfsense", {
   }): Promise<void> => ipcRenderer.invoke("shell:titlebar-overlay", overlay),
   openExternal: (url: string): Promise<void> =>
     ipcRenderer.invoke("shell:open-external", url),
+  theme: {
+    set: (theme: "dark" | "light" | "system"): Promise<void> =>
+      ipcRenderer.invoke("theme:set", theme),
+    getSystemTheme: (): "dark" | "light" => systemTheme,
+    onSystemThemeChange: (
+      listener: (theme: "dark" | "light") => void
+    ): (() => void) => {
+      const wrapped = (_event: unknown, theme: unknown) => {
+        if (theme === "dark" || theme === "light") listener(theme)
+      }
+      ipcRenderer.on("theme:system-changed", wrapped)
+      return () => ipcRenderer.removeListener("theme:system-changed", wrapped)
+    },
+  },
 })
diff --git a/surfsense_local/frontend/index.html b/surfsense_local/frontend/index.html
index 87b2962035..b0dba5c141 100644
--- a/surfsense_local/frontend/index.html
+++ b/surfsense_local/frontend/index.html
@@ -2,6 +2,33 @@
 <html lang="en">
   <head>
     <meta charset="UTF-8" />
+    <!--
+      Blocking, mirrors ThemeProvider's resolution logic (theme-provider.tsx)
+      so the correct theme paints in the first frame instead of flashing light
+      while the bundle loads and the ThemeProvider effect runs. Must stay in
+      sync with THEME_STORAGE_KEY / getSystemTheme there. window.surfsense is
+      already available here: preload runs before this script.
+    -->
+    <script>
+      ;(() => {
+        try {
+          const storageKey = "surfsense:theme:v1"
+          const stored = localStorage.getItem(storageKey)
+          const systemTheme = window.surfsense?.theme?.getSystemTheme
+            ? window.surfsense.theme.getSystemTheme()
+            : window.matchMedia("(prefers-color-scheme: dark)").matches
+              ? "dark"
+              : "light"
+          const theme =
+            stored === "light" || stored === "dark" ? stored : systemTheme
+          const root = document.documentElement
+          root.classList.add(theme)
+          root.style.colorScheme = theme
+        } catch {
+          // no-op: fall back to the CSS defaults if storage/matchMedia throws
+        }
+      })()
+    </script>
     <link rel="icon" type="image/svg+xml" href="/vite.svg" />
     <meta name="viewport" content="width=device-width, initial-scale=1.0" />
     <title>SurfSense Community Local</title>
diff --git a/surfsense_local/frontend/src/components/theme-provider.tsx b/surfsense_local/frontend/src/components/theme-provider.tsx
index 790944206b..735047f26b 100644
--- a/surfsense_local/frontend/src/components/theme-provider.tsx
+++ b/surfsense_local/frontend/src/components/theme-provider.tsx
@@ -32,6 +32,12 @@ function isTheme(value: string | null): value is Theme {
   return THEME_VALUES.includes(value as Theme)
 }
 
+function syncMainProcessTheme(theme: Theme) {
+  // Lets main pick a matching BrowserWindow backgroundColor, so the next
+  // reload/launch doesn't flash the wrong theme before this effect can run.
+  void window.surfsense?.theme?.set(theme)
+}
+
 function syncTitleBarOverlay(theme: ResolvedTheme) {
   const platform = window.surfsense?.platform
   if (platform !== "win32" && platform !== "linux") {
@@ -45,11 +51,15 @@ function syncTitleBarOverlay(theme: ResolvedTheme) {
 }
 
 function getSystemTheme(): ResolvedTheme {
-  if (window.matchMedia(COLOR_SCHEME_QUERY).matches) {
-    return "dark"
+  // nativeTheme (main process) is authoritative when running in Electron;
+  // matchMedia is only a fallback for environments without the bridge
+  // (tests, a bare `vite` preview outside the app shell).
+  const fromMain = window.surfsense?.theme?.getSystemTheme?.()
+  if (fromMain === "dark" || fromMain === "light") {
+    return fromMain
   }
 
-  return "light"
+  return window.matchMedia(COLOR_SCHEME_QUERY).matches ? "dark" : "light"
 }
 
 function disableTransitionsTemporarily() {
@@ -126,6 +136,7 @@ export function ThemeProvider({
       root.classList.remove("light", "dark")
       root.classList.add(resolvedTheme)
       syncTitleBarOverlay(resolvedTheme)
+      syncMainProcessTheme(nextTheme)
 
       if (restoreTransitions) {
         restoreTransitions()
@@ -141,11 +152,16 @@ export function ThemeProvider({
       return undefined
     }
 
-    const mediaQuery = window.matchMedia(COLOR_SCHEME_QUERY)
     const handleChange = () => {
       applyTheme("system")
     }
 
+    const onSystemThemeChange = window.surfsense?.theme?.onSystemThemeChange
+    if (onSystemThemeChange) {
+      return onSystemThemeChange(handleChange)
+    }
+
+    const mediaQuery = window.matchMedia(COLOR_SCHEME_QUERY)
     mediaQuery.addEventListener("change", handleChange)
 
     return () => {
diff --git a/surfsense_local/frontend/src/features/onboarding/onboarding-page.tsx b/surfsense_local/frontend/src/features/onboarding/onboarding-page.tsx
index ac3f0cd3a4..e571a1cba6 100644
--- a/surfsense_local/frontend/src/features/onboarding/onboarding-page.tsx
+++ b/surfsense_local/frontend/src/features/onboarding/onboarding-page.tsx
@@ -76,8 +76,7 @@ function WelcomeStep({ onNext }: { onNext: () => void }) {
         </CardTitle>
         <CardDescription className="mx-auto max-w-md text-pretty">
           SurfSense turns scattered documents, notes, and sources into one
-          searchable workspace. Nothing leaves this computer until you allow it;
-          you will be asked the first time.
+          searchable workspace. Nothing leaves your machine without asking first.
         </CardDescription>
       </CardHeader>
       <CardFooter className="justify-center border-t-0 bg-transparent">
diff --git a/surfsense_local/frontend/src/lib/api.ts b/surfsense_local/frontend/src/lib/api.ts
index 3da5a1d9ee..a0d08488b0 100644
--- a/surfsense_local/frontend/src/lib/api.ts
+++ b/surfsense_local/frontend/src/lib/api.ts
@@ -25,6 +25,13 @@ declare global {
         symbolColor: string
       }) => Promise<void>
       openExternal?: (url: string) => Promise<void>
+      theme?: {
+        set: (theme: "dark" | "light" | "system") => Promise<void>
+        getSystemTheme: () => "dark" | "light"
+        onSystemThemeChange: (
+          listener: (theme: "dark" | "light") => void
+        ) => () => void
+      }
     }
   }
 }