diff --git a/README.md b/README.md
index 49ae306..f1c55b8 100644
--- a/README.md
+++ b/README.md
@@ -4,7 +4,7 @@
 
 Raidy is a raid scheduling project for Discord statics: the web console is where everyone plans, and Discord carries the announcements. One Go process runs the Discord bot, web API, scheduler, and production web assets, backed by PostgreSQL.
 
-**Status:** `v0.0.19` is an early development snapshot.
+**Status:** `v0.0.20` is an early development snapshot.
 
 ```text
 backend/     Go service, Discord interactions, web API, PostgreSQL migrations
diff --git a/web/e2e/product.spec.ts b/web/e2e/product.spec.ts
index 6dc0c91..f2fc62a 100644
--- a/web/e2e/product.spec.ts
+++ b/web/e2e/product.spec.ts
@@ -42,3 +42,17 @@ test("the page never scrolls sideways on a phone", async ({ browser }) => {
   const overflow = await page.evaluate(() => document.documentElement.scrollWidth - window.innerWidth);
   expect(overflow).toBeLessThanOrEqual(0);
 });
+
+test("the theme switch overrides the system and carries over to the demo", async ({ page }) => {
+  await page.emulateMedia({ colorScheme: "dark" });
+  await page.goto("/");
+  const html = page.locator("html");
+  await expect(html).toHaveClass(/dark/);
+  await page.getByRole("radio", { name: "Light theme" }).click();
+  await expect(html).not.toHaveClass(/dark/);
+  await page.reload();
+  await expect(html).not.toHaveClass(/dark/);
+  await page.getByRole("link", { name: "Try the demo" }).click();
+  await expect(page.getByRole("table", { name: /availability/i })).toBeVisible({ timeout: 30_000 });
+  await expect(html).not.toHaveClass(/dark/);
+});
diff --git a/web/package-lock.json b/web/package-lock.json
index fea1fed..29caa32 100644
--- a/web/package-lock.json
+++ b/web/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "raidy-web",
-  "version": "0.0.19",
+  "version": "0.0.20",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "raidy-web",
-      "version": "0.0.19",
+      "version": "0.0.20",
       "dependencies": {
         "@fontsource-variable/geist": "^5.3.0",
         "@fontsource-variable/geist-mono": "^5.3.0",
diff --git a/web/package.json b/web/package.json
index 9677871..823cc9c 100644
--- a/web/package.json
+++ b/web/package.json
@@ -1,7 +1,7 @@
 {
   "name": "raidy-web",
   "private": true,
-  "version": "0.0.19",
+  "version": "0.0.20",
   "type": "module",
   "scripts": {
     "dev": "vite",
diff --git a/web/product/index.html b/web/product/index.html
index 21654a2..21259d9 100644
--- a/web/product/index.html
+++ b/web/product/index.html
@@ -17,9 +17,20 @@
     <link rel="icon" type="image/svg+xml" href="/favicon.svg" />
     <script>
       (() => {
-        const dark = matchMedia("(prefers-color-scheme: dark)").matches;
-        document.documentElement.classList.toggle("dark", dark);
-        document.querySelector('meta[name="theme-color"]').content = dark ? "#121110" : "#fafaf9";
+        let preference = "system";
+        try {
+          preference = localStorage.getItem("raidy-theme") || "system";
+        } catch {}
+        const theme =
+          preference === "system"
+            ? matchMedia("(prefers-color-scheme: dark)").matches
+              ? "dark"
+              : "light"
+            : preference;
+        document.documentElement.dataset.themePreference = preference;
+        document.documentElement.dataset.theme = theme;
+        document.documentElement.classList.toggle("dark", theme === "dark");
+        document.querySelector('meta[name="theme-color"]').content = theme === "dark" ? "#121110" : "#fafaf9";
       })();
     </script>
   </head>
diff --git a/web/src/App.tsx b/web/src/App.tsx
index c73e6a8..9620cc1 100644
--- a/web/src/App.tsx
+++ b/web/src/App.tsx
@@ -11,7 +11,7 @@ import { SchedulePanel } from "@/features/schedule/schedule-panel";
 import { TeamPanel } from "@/features/team/team-panel";
 import { message } from "@/lib/format";
 import { isDemo, productURL, teamURL } from "@/lib/paths";
-import { applyTheme, type Theme, type ThemePreference } from "@/lib/theme";
+import { useTheme } from "@/lib/theme";
 import { cn } from "@/lib/utils";
 
 type Tab = "overview" | "schedule" | "team";
@@ -33,11 +33,7 @@ export default function App() {
   const [loading, setLoading] = useState(true);
   const [error, setError] = useState("");
   const [revision, setRevision] = useState(0);
-  const [themePreference, setThemePreference] = useState<ThemePreference>(() => {
-    const saved = document.documentElement.dataset.themePreference;
-    return saved === "light" || saved === "dark" ? saved : "system";
-  });
-  const [resolvedTheme, setResolvedTheme] = useState<Theme>("light");
+  const { preference: themePreference, resolved: resolvedTheme, choose: chooseTheme } = useTheme();
 
   async function loadData(preferred?: number) {
     const [nextTeams, nextGuilds] = await Promise.all([api<Team[]>("/api/teams"), api<Guild[]>("/api/guilds")]);
@@ -68,18 +64,6 @@ export default function App() {
     })();
   }, []);
 
-  useEffect(() => {
-    const media = matchMedia("(prefers-color-scheme: dark)");
-    const update = () => {
-      const theme = themePreference === "system" ? (media.matches ? "dark" : "light") : themePreference;
-      applyTheme(theme);
-      setResolvedTheme(theme);
-    };
-    update();
-    if (themePreference === "system") media.addEventListener("change", update);
-    return () => media.removeEventListener("change", update);
-  }, [themePreference]);
-
   const selected = teams.find((team) => team.id === teamID) ?? null;
 
   function selectTeam(id: number) {
@@ -100,16 +84,6 @@ export default function App() {
     location.assign(isDemo ? productURL : "/");
   }
 
-  function chooseTheme(next: ThemePreference) {
-    document.documentElement.dataset.themePreference = next;
-    try {
-      localStorage.setItem("raidy-theme", next);
-    } catch {
-      /* Theme still applies for this page. */
-    }
-    setThemePreference(next);
-  }
-
   const toaster = <Toaster theme={resolvedTheme} position="bottom-right" toastOptions={{ className: "font-sans" }} />;
 
   if (loading) return <Loading />;
diff --git a/web/src/lib/theme.ts b/web/src/lib/theme.ts
index 93e1378..dd1e86e 100644
--- a/web/src/lib/theme.ts
+++ b/web/src/lib/theme.ts
@@ -1,3 +1,5 @@
+import { useEffect, useState } from "react";
+
 export type Theme = "light" | "dark";
 
 export type ThemePreference = Theme | "system";
@@ -9,3 +11,39 @@ export function applyTheme(theme: Theme) {
     .querySelector<HTMLMetaElement>('meta[name="theme-color"]')
     ?.setAttribute("content", theme === "dark" ? "#121110" : "#fafaf9");
 }
+
+/**
+ * The viewer's theme choice (System, Light or Dark), saved per browser and
+ * shared by every page on the site, and the theme it resolves to.
+ */
+export function useTheme() {
+  const [preference, setPreference] = useState<ThemePreference>(() => {
+    const saved = document.documentElement.dataset.themePreference;
+    return saved === "light" || saved === "dark" ? saved : "system";
+  });
+  const [resolved, setResolved] = useState<Theme>("light");
+
+  useEffect(() => {
+    const media = matchMedia("(prefers-color-scheme: dark)");
+    const update = () => {
+      const theme = preference === "system" ? (media.matches ? "dark" : "light") : preference;
+      applyTheme(theme);
+      setResolved(theme);
+    };
+    update();
+    if (preference === "system") media.addEventListener("change", update);
+    return () => media.removeEventListener("change", update);
+  }, [preference]);
+
+  function choose(next: ThemePreference) {
+    document.documentElement.dataset.themePreference = next;
+    try {
+      localStorage.setItem("raidy-theme", next);
+    } catch {
+      /* Theme still applies for this page. */
+    }
+    setPreference(next);
+  }
+
+  return { preference, resolved, choose };
+}
diff --git a/web/src/product/product-page.tsx b/web/src/product/product-page.tsx
index 74ffd2b..7728254 100644
--- a/web/src/product/product-page.tsx
+++ b/web/src/product/product-page.tsx
@@ -1,6 +1,9 @@
 import { CalendarClock, CalendarSync, Globe, MessageSquareText, MousePointerClick, ShieldCheck } from "lucide-react";
 import { Wordmark } from "@/components/common";
+import { cn } from "@/lib/utils";
 import { Button } from "@/components/ui/button";
+import { ThemeToggle } from "@/components/user-menu";
+import { type Theme, useTheme } from "@/lib/theme";
 import { HeroDemo } from "./hero-demo";
 
 const github = "https://github.com/joshchen-dev/raidy";
@@ -64,6 +67,7 @@ const questions = [
 ];
 
 export function ProductPage() {
+  const theme = useTheme();
   return (
     <div className="min-h-screen bg-background text-foreground">
       <header className="mx-auto flex h-16 max-w-6xl items-center gap-6 px-4 sm:px-6">
@@ -81,9 +85,14 @@ export function ProductPage() {
             FAQ
           </a>
         </nav>
-        <Button asChild size="sm" className="ml-auto">
-          <a href="demo/">Try the demo</a>
-        </Button>
+        <div className="ml-auto flex items-center gap-3">
+          <div className="hidden sm:block">
+            <ThemeToggle value={theme.preference} onChange={theme.choose} />
+          </div>
+          <Button asChild size="sm">
+            <a href="demo/">Try the demo</a>
+          </Button>
+        </div>
       </header>
 
       <main>
@@ -145,8 +154,12 @@ export function ProductPage() {
               Inside the app
             </h2>
             <div className="mt-12 grid items-end gap-6 lg:grid-cols-[minmax(0,1fr)_280px]">
-              <Screen name="schedule" alt="The schedule editor with raid days, times and a preview of the first week" />
-              <Screen name="mobile" alt="The availability grid on a phone" narrow />
+              <Screen
+                theme={theme.resolved}
+                name="schedule"
+                alt="The schedule editor with raid days, times and a preview of the first week"
+              />
+              <Screen theme={theme.resolved} name="mobile" alt="The availability grid on a phone" narrow />
             </div>
           </div>
         </section>
@@ -194,6 +207,9 @@ export function ProductPage() {
       </main>
 
       <footer className="mx-auto flex max-w-6xl flex-wrap items-center gap-x-6 gap-y-2 px-4 py-8 text-sm text-muted-foreground sm:px-6">
+        <div className="w-full sm:hidden">
+          <ThemeToggle value={theme.preference} onChange={theme.choose} />
+        </div>
         <Wordmark />
         <a className="hover:text-foreground" href={github}>
           GitHub
@@ -206,17 +222,17 @@ export function ProductPage() {
   );
 }
 
-/** A screenshot of the real app, in the viewer's color scheme. */
-function Screen({ name, alt, narrow = false }: { name: string; alt: string; narrow?: boolean }) {
+/** A screenshot of the real app, in the page's current theme. */
+function Screen({ theme, name, alt, narrow = false }: { theme: Theme; name: string; alt: string; narrow?: boolean }) {
   return (
-    <picture className={narrow ? "mx-auto block w-full max-w-[280px]" : "block"}>
-      <source srcSet={`screens/${name}-dark.png`} media="(prefers-color-scheme: dark)" />
-      <img
-        src={`screens/${name}-light.png`}
-        alt={alt}
-        loading="lazy"
-        className="w-full rounded-lg border bg-card shadow-[0_24px_48px_-24px_rgb(28_25_23/0.25)]"
-      />
-    </picture>
+    <img
+      src={`screens/${name}-${theme}.png`}
+      alt={alt}
+      loading="lazy"
+      className={cn(
+        "w-full rounded-lg border bg-card shadow-[0_24px_48px_-24px_rgb(28_25_23/0.25)]",
+        narrow && "mx-auto max-w-[280px]"
+      )}
+    />
   );
 }