feat: add theme switcher with system/light/dark segmented control (#75)

* feat: add theme switcher with system/light/dark segmented control

Add a three-way theme toggle (system, light, dark) as a segmented
icon control in the account dropdown menu. Rename placeholder daisyUI
theme names from "todo" to "openseo".

* refactor: always resolve data-theme explicitly, remove duplicated dark CSS

Instead of removing data-theme in "system" mode and relying on
@media (prefers-color-scheme: dark) CSS, always resolve to an
explicit theme name via matchMedia. This eliminates the duplicated
dark-mode CSS overrides.

src/client/components/ThemePreferenceMenuItems.tsx

@@ -0,0 +1,60 @@
+import { Monitor, Moon, Sun } from "lucide-react";
+import { type ThemePreference, useThemePreference } from "@/client/lib/theme";
+
+const THEME_OPTIONS: {
+  value: ThemePreference;
+  label: string;
+  icon: typeof Sun;
+}[] = [
+  { value: "system", label: "System", icon: Monitor },
+  { value: "light", label: "Light", icon: Sun },
+  { value: "dark", label: "Dark", icon: Moon },
+];
+
+export function ThemePreferenceMenuItems() {
+  const { themePreference, setThemePreference } = useThemePreference();
+
+  return (
+    <>
+      <li className="menu-title pt-2">
+        <span>Theme</span>
+      </li>
+
+      <li>
+        <div
+          role="radiogroup"
+          aria-label="Theme preference"
+          className="flex gap-0.5 rounded-lg bg-base-200 p-0.5"
+        >
+          {THEME_OPTIONS.map((option) => {
+            const isActive = option.value === themePreference;
+            const Icon = option.icon;
+
+            return (
+              <div
+                key={option.value}
+                className="tooltip tooltip-bottom flex flex-1 before:whitespace-nowrap"
+                data-tip={option.label}
+              >
+                <button
+                  type="button"
+                  role="radio"
+                  aria-checked={isActive}
+                  aria-label={option.label}
+                  className={`flex flex-1 items-center justify-center rounded-md px-2.5 py-1.5 transition-colors ${
+                    isActive
+                      ? "bg-base-100 text-base-content shadow-sm"
+                      : "text-base-content/50 hover:text-base-content/80"
+                  }`}
+                  onClick={() => setThemePreference(option.value)}
+                >
+                  <Icon className="size-4" />
+                </button>
+              </div>
+            );
+          })}
+        </div>
+      </li>
+    </>
+  );
+}

src/client/layout/AppShell.tsx

@@ -6,6 +6,7 @@ import {
   MissingSeoSetupModal,
   SeoApiStatusBanners,
 } from "@/client/layout/AppShellParts";
+import { ThemePreferenceMenuItems } from "@/client/components/ThemePreferenceMenuItems";
 import { getProjectNavItems } from "@/client/navigation/items";
 import { getSignInHrefForLocation } from "@/lib/auth-redirect";
 import { authClient, useSession } from "@/lib/auth-client";
@@ -208,26 +209,19 @@ function TopNav({
             </button>
           </div>
 
-          <HostedSessionActions />
+          <AccountMenu />
         </div>
       </div>
 
-      <HostedSessionActions mobileOnly />
+      <AccountMenu mobileOnly />
     </div>
   );
 }
 
-function HostedSessionActions({
-  mobileOnly = false,
-}: {
-  mobileOnly?: boolean;
-}) {
+function AccountMenu({ mobileOnly = false }: { mobileOnly?: boolean }) {
   const { data: session } = useSession();
   const isHostedMode = isHostedClientAuthMode();
-
-  if (!isHostedMode || !session?.user?.email) {
-    return null;
-  }
+  const email = session?.user?.email;
 
   const handleSignOut = () => {
     const signInHref = getSignInHrefForLocation(window.location);
@@ -255,17 +249,21 @@ function HostedSessionActions({
           tabIndex={0}
           className="dropdown-content z-20 menu mt-3 min-w-56 rounded-box border border-base-300 bg-base-100 p-2 shadow-lg"
         >
+          {email ? (
             <li className="menu-title max-w-full">
-            <span className="truncate text-base-content">
-              {session.user.email}
-            </span>
+              <span className="truncate text-base-content">{email}</span>
             </li>
+          ) : null}
+          <ThemePreferenceMenuItems />
+          {isHostedMode ? (
             <li>
               <a href={BILLING_ROUTE} className="flex items-center gap-2">
                 <CreditCard className="h-4 w-4" />
                 Billing
               </a>
             </li>
+          ) : null}
+          {isHostedMode && email ? (
             <li>
               <button
                 type="button"
@@ -275,6 +273,7 @@ function HostedSessionActions({
                 Sign out
               </button>
             </li>
+          ) : null}
         </ul>
       </div>
     </div>

src/client/lib/theme.ts

@@ -0,0 +1,133 @@
+import * as React from "react";
+
+export type ThemePreference = "system" | "light" | "dark";
+
+const LIGHT_THEME_NAME = "openseo";
+const DARK_THEME_NAME = "openseo-dark";
+
+const THEME_STORAGE_KEY = "theme-preference";
+const THEME_CHANGE_EVENT = "theme-preference-change";
+
+function readThemePreference(): ThemePreference {
+  if (typeof window === "undefined") {
+    return "system";
+  }
+
+  try {
+    const stored = window.localStorage.getItem(THEME_STORAGE_KEY);
+    if (stored === "light" || stored === "dark") {
+      return stored;
+    }
+    return "system";
+  } catch {
+    return "system";
+  }
+}
+
+function writeThemePreference(themePreference: ThemePreference) {
+  try {
+    if (themePreference === "system") {
+      window.localStorage.removeItem(THEME_STORAGE_KEY);
+    } else {
+      window.localStorage.setItem(THEME_STORAGE_KEY, themePreference);
+    }
+  } catch {
+    // localStorage can be unavailable in private browsing or strict browser modes.
+  }
+}
+
+function resolveThemeName(themePreference: ThemePreference): string {
+  if (themePreference === "light") return LIGHT_THEME_NAME;
+  if (themePreference === "dark") return DARK_THEME_NAME;
+
+  // "system" — resolve from OS preference
+  if (
+    typeof window !== "undefined" &&
+    window.matchMedia("(prefers-color-scheme: dark)").matches
+  ) {
+    return DARK_THEME_NAME;
+  }
+  return LIGHT_THEME_NAME;
+}
+
+function applyThemePreference(themePreference: ThemePreference) {
+  if (typeof document === "undefined") {
+    return;
+  }
+
+  document.documentElement.setAttribute(
+    "data-theme",
+    resolveThemeName(themePreference),
+  );
+}
+
+function subscribeToThemePreference(onStoreChange: () => void) {
+  if (typeof window === "undefined") {
+    return () => {};
+  }
+
+  const handleThemeChange = () => {
+    onStoreChange();
+  };
+
+  const handleStorage = (event: StorageEvent) => {
+    if (event.key && event.key !== THEME_STORAGE_KEY) {
+      return;
+    }
+
+    onStoreChange();
+  };
+
+  const mediaQuery = window.matchMedia("(prefers-color-scheme: dark)");
+  const handleMediaChange = () => {
+    // Re-apply when OS preference changes so "system" mode stays in sync
+    applyThemePreference(readThemePreference());
+    onStoreChange();
+  };
+
+  window.addEventListener(THEME_CHANGE_EVENT, handleThemeChange);
+  window.addEventListener("storage", handleStorage);
+  mediaQuery.addEventListener("change", handleMediaChange);
+
+  return () => {
+    window.removeEventListener(THEME_CHANGE_EVENT, handleThemeChange);
+    window.removeEventListener("storage", handleStorage);
+    mediaQuery.removeEventListener("change", handleMediaChange);
+  };
+}
+
+export function useThemePreference() {
+  const themePreference = React.useSyncExternalStore<ThemePreference>(
+    subscribeToThemePreference,
+    readThemePreference,
+    () => "system",
+  );
+
+  React.useEffect(() => {
+    applyThemePreference(themePreference);
+  }, [themePreference]);
+
+  const setThemePreference = React.useCallback(
+    (nextThemePreference: ThemePreference) => {
+      writeThemePreference(nextThemePreference);
+      applyThemePreference(nextThemePreference);
+      window.dispatchEvent(new Event(THEME_CHANGE_EVENT));
+    },
+    [],
+  );
+
+  return { themePreference, setThemePreference };
+}
+
+export const themePreferenceInitScript = `(() => {
+  try {
+    var p = window.localStorage.getItem(${JSON.stringify(THEME_STORAGE_KEY)});
+    var t;
+    if (p === "light") t = ${JSON.stringify(LIGHT_THEME_NAME)};
+    else if (p === "dark") t = ${JSON.stringify(DARK_THEME_NAME)};
+    else t = window.matchMedia("(prefers-color-scheme: dark)").matches ? ${JSON.stringify(DARK_THEME_NAME)} : ${JSON.stringify(LIGHT_THEME_NAME)};
+    document.documentElement.setAttribute("data-theme", t);
+  } catch {
+    document.documentElement.setAttribute("data-theme", ${JSON.stringify(LIGHT_THEME_NAME)});
+  }
+})();`;

src/client/styles/app.css

@@ -22,7 +22,7 @@
 
 /* Light theme */
 @plugin "daisyui/theme" {
-  name: "todo";
+  name: "openseo";
   default: true;
   prefersdark: false;
   color-scheme: light;
@@ -58,7 +58,7 @@
 
 /* Dark theme - auto-activates via prefers-color-scheme */
 @plugin "daisyui/theme" {
-  name: "todo-dark";
+  name: "openseo-dark";
   prefersdark: true;
   color-scheme: dark;
   --color-base-100: oklch(18% 0 0);
@@ -198,8 +198,7 @@ select {
   background-color: #dc2626;
 }
 
-@media (prefers-color-scheme: dark) {
-  :root {
+html[data-theme="openseo-dark"] {
   --trend-grid-color: oklch(78% 0.01 255 / 0.22);
   --trend-axis-color: oklch(84% 0.01 255 / 0.62);
   --trend-fill-start-opacity: 0.24;
@@ -209,48 +208,47 @@ select {
   --trend-tooltip-shadow: oklch(0% 0 0 / 0.35);
 }
 
-  .score-badge {
+html[data-theme="openseo-dark"] .score-badge {
   color: oklch(96% 0.01 95);
   filter: saturate(1.26) brightness(1.14);
 }
 
-  .score-tier-1 {
+html[data-theme="openseo-dark"] .score-tier-1 {
   background-color: oklch(58% 0.12 148);
 }
 
-  .score-tier-2 {
+html[data-theme="openseo-dark"] .score-tier-2 {
   background-color: oklch(60% 0.115 132);
 }
 
-  .score-tier-3 {
+html[data-theme="openseo-dark"] .score-tier-3 {
   background-color: oklch(66% 0.11 92);
 }
 
-  .score-tier-4 {
+html[data-theme="openseo-dark"] .score-tier-4 {
   background-color: oklch(64% 0.12 56);
 }
 
-  .score-tier-5 {
+html[data-theme="openseo-dark"] .score-tier-5 {
   background-color: oklch(62% 0.12 36);
 }
 
-  .score-tier-6 {
+html[data-theme="openseo-dark"] .score-tier-6 {
   background-color: oklch(58% 0.11 30);
 }
 
-  .alert-warning {
+html[data-theme="openseo-dark"] .alert-warning {
   @apply border-warning/60 bg-warning/20;
 }
 
-  .alert-info {
+html[data-theme="openseo-dark"] .alert-info {
   @apply border-info/60 bg-info/20;
 }
 
-  .alert-success {
+html[data-theme="openseo-dark"] .alert-success {
   @apply border-success/60 bg-success/20;
 }
 
-  .alert-error {
+html[data-theme="openseo-dark"] .alert-error {
   @apply border-error/60 bg-error/20;
 }
-}

src/routes/__root.tsx

@@ -11,6 +11,7 @@ import { TanStackDevtools } from "@tanstack/react-devtools";
 import { QueryClientProvider } from "@tanstack/react-query";
 import * as React from "react";
 import { DefaultCatchBoundary } from "@/client/components/DefaultCatchBoundary";
+import { themePreferenceInitScript } from "@/client/lib/theme";
 import { initPostHog } from "@/client/lib/posthog";
 import { NotFound } from "@/client/components/NotFound";
 import appCss from "@/client/styles/app.css?url";
@@ -93,8 +94,11 @@ function RootDocument({ children }: { children: React.ReactNode }) {
     import.meta.env.DEV && import.meta.env.VITE_SHOW_DEVTOOLS !== "false";
 
   return (
-    <html>
+    <html suppressHydrationWarning>
       <head>
+        <script
+          dangerouslySetInnerHTML={{ __html: themePreferenceInitScript }}
+        />
         <HeadContent />
       </head>
       <body>

src/routes/_authenticated.subscribe.tsx

@@ -2,6 +2,7 @@ import { createFileRoute, useNavigate } from "@tanstack/react-router";
 import { AutumnProvider, useCustomer } from "autumn-js/react";
 import { useEffect, useState } from "react";
 import { User } from "lucide-react";
+import { ThemePreferenceMenuItems } from "@/client/components/ThemePreferenceMenuItems";
 import { authClient, useSession } from "@/lib/auth-client";
 import { getSignInHrefForLocation } from "@/lib/auth-redirect";
 import { getStandardErrorMessage } from "@/client/lib/error-messages";
@@ -164,11 +165,7 @@ function SubscribePageContent() {
   );
 }
 
-function SubscribePageAccountMenu({
-  email,
-}: {
-  email: string | undefined;
-}) {
+function SubscribePageAccountMenu({ email }: { email: string | undefined }) {
   if (!email) return null;
 
   const handleSignOut = () => {
@@ -200,6 +197,7 @@ function SubscribePageAccountMenu({
           <li className="menu-title max-w-full">
             <span className="truncate text-base-content">{email}</span>
           </li>
+          <ThemePreferenceMenuItems />
           <li>
             <button
               type="button"