diff --git a/src/components/Navbar.jsx b/src/components/Navbar.jsx
index 8ef775d0..cd9505e5 100644
--- a/src/components/Navbar.jsx
+++ b/src/components/Navbar.jsx
@@ -1,12 +1,31 @@
-import { useState } from "react";
+import { useState, useEffect } from "react";
 import { Link } from "react-router-dom";
 import logo from "../assets/logo_light_160.png";
 import { SideSheet } from "@douyinfe/semi-ui";
 import { IconMenu } from "@douyinfe/semi-icons";
 import { socials } from "../data/socials";
+import { getTheme, toggleTheme, onSystemPrefChange } from "../theme";
 
 export default function Navbar() {
   const [openMenu, setOpenMenu] = useState(false);
+  const [isDark, setIsDark] = useState(() => getTheme() === "dark");
+
+  useEffect(() => {
+    // Keep local state synced when system preference changes (only when user hasn't chosen a theme)
+    const unsubscribe = onSystemPrefChange((prefersDark) => {
+      // if there's an explicit stored preference, ignore system changes
+      try {
+        const stored = window.localStorage && window.localStorage.getItem("drawdb:theme");
+        if (!stored) {
+          setIsDark(prefersDark);
+        }
+      } catch (e) {
+        // ignore storage errors
+      }
+    });
+
+    return () => unsubscribe && unsubscribe();
+  }, []);
 
   return (
     <>
@@ -75,12 +94,48 @@ export default function Navbar() {
             </a>
           </div>
         </div>
-        <button
-          onClick={() => setOpenMenu((prev) => !prev)}
-          className="hidden md:inline-block h-[24px]"
-        >
-          <IconMenu size="extra-large" />
-        </button>
+        <div className="flex items-center gap-4">
+          <button
+            onClick={() => {
+              const next = toggleTheme();
+              setIsDark(next === "dark");
+            }}
+            role="switch"
+            aria-checked={isDark}
+            aria-label="Toggle dark mode"
+            className="inline-flex relative items-center justify-center w-10 h-10 rounded-full focus:outline-none focus:ring-2 focus:ring-sky-500"
+            title="Toggle theme"
+          >
+            {/* Sun / Moon SVGs — visible depending on state */}
+            <svg
+              className={`w-5 h-5 transition-opacity duration-200 ${isDark ? "opacity-0" : "opacity-100"}`}
+              viewBox="0 0 24 24"
+              fill="none"
+              xmlns="http://www.w3.org/2000/svg"
+              aria-hidden="true"
+            >
+              <path d="M12 4V2M12 22v-2M4 12H2M22 12h-2M5 5l-1.5-1.5M20.5 20.5 19 19M19 5l1.5-1.5M4.5 19.5 6 18" stroke="currentColor" strokeWidth="1.5" strokeLinecap="round" strokeLinejoin="round"/>
+              <circle cx="12" cy="12" r="3" stroke="currentColor" strokeWidth="1.5"/>
+            </svg>
+            <svg
+              className={`w-5 h-5 absolute transition-opacity duration-200 ${isDark ? "opacity-100" : "opacity-0"}`}
+              viewBox="0 0 24 24"
+              fill="none"
+              xmlns="http://www.w3.org/2000/svg"
+              aria-hidden="true"
+            >
+              <path d="M21 12.79A9 9 0 1111.21 3 7 7 0 0021 12.79z" stroke="currentColor" strokeWidth="1.5" strokeLinecap="round" strokeLinejoin="round"/>
+            </svg>
+          </button>
+
+          <button
+            onClick={() => setOpenMenu((prev) => !prev)}
+            className="hidden md:inline-block h-[24px]"
+            aria-label="Open menu"
+          >
+            <IconMenu size="extra-large" />
+          </button>
+        </div>
       </div>
       <hr />
       <SideSheet
diff --git a/src/index.css b/src/index.css
index 44dabcd0..52f068b6 100644
--- a/src/index.css
+++ b/src/index.css
@@ -36,6 +36,76 @@
   }
 }
 
+/* Theme variables --------------------------------------------------------- */
+:root {
+  /* default (light) values — may be overridden by .theme-dark */
+  --bg: 255 255 255;
+  --text: 17 24 39; /* slate-900 */
+  --muted: 107 114 128; /* slate-500 */
+  --accent: 14 165 233; /* sky-400 */
+  --semi-grey-0: 255,255,255;
+  --semi-grey-1: 249,250,251;
+  --semi-grey-2: 241,245,249;
+  --semi-grey-3: 226,232,240;
+  --semi-grey-4: 203,213,225;
+  --semi-grey-9: 30,41,59;
+  --semi-blue-5: 14,165,233;
+  --semi-blue-6: 2,132,199;
+  --semi-color-text-1: rgb(var(--text));
+  --semi-color-bg-0: rgb(var(--bg));
+  --semi-color-bg-2: rgb(var(--bg));
+  --semi-color-bg-3: rgb(var(--bg));
+}
+
+/* Dark theme overrides */
+.theme-dark,
+html.theme-dark {
+  --bg: 17 24 39; /* slate-900 */
+  --text: 243 244 246; /* slate-50 */
+  --muted: 148 163 184; /* slate-400 */
+  --accent: 56 189 248; /* sky-400 bright */
+  --semi-grey-0: 17,24,39;
+  --semi-grey-1: 20,23,29;
+  --semi-grey-2: 30,41,59;
+  --semi-grey-3: 39,47,61;
+  --semi-grey-4: 55,65,81;
+  --semi-grey-9: 243,244,246;
+  --semi-blue-5: 56,189,248;
+  --semi-blue-6: 14,165,233;
+  --semi-color-text-1: rgb(var(--text));
+  --semi-color-bg-0: rgb(var(--bg));
+  --semi-color-bg-2: rgb(var(--bg));
+  --semi-color-bg-3: rgb(var(--bg));
+}
+
+/* Light theme explicit class (optional; root defaults to light) */
+.theme-light,
+html.theme-light {
+  /* no-op; variables already set in :root for light */
+}
+
+/* apply variables to body for layout */
+body {
+  background-color: rgb(var(--bg));
+  color: rgb(var(--text));
+}
+
+/* Reduced motion: disable transitions */
+@media (prefers-reduced-motion: reduce) {
+  * {
+    transition: none !important;
+    animation: none !important;
+  }
+}
+
+/* Subtle color transition when toggling theme */
+@media (prefers-reduced-motion: no-preference) {
+  :root,
+  html {
+    transition: color 220ms ease, background-color 220ms ease;
+  }
+}
+
 .semi-form-vertical .semi-form-field {
   margin: 0;
   padding-top: 8px !important;
diff --git a/src/pages/THEME_TOGGLE.md b/src/pages/THEME_TOGGLE.md
new file mode 100644
index 00000000..d03721ac
--- /dev/null
+++ b/src/pages/THEME_TOGGLE.md
@@ -0,0 +1,9 @@
+Theme toggle (light / dark)
+--------------------------------
+
+The landing page includes a theme toggle in the top-right header. It persists the user's choice in localStorage using the key `drawdb:theme` and falls back to the system preference; if neither is available the default is dark.
+
+Files:
+- `src/theme.js` — theme helper (init, toggle, storage, system listener)
+- `src/components/Navbar.jsx` — toggle button UI and ARIA attributes
+- `src/index.css` — CSS variables and `.theme-dark` / `.theme-light` classes
diff --git a/src/theme.js b/src/theme.js
new file mode 100644
index 00000000..09cfacf8
--- /dev/null
+++ b/src/theme.js
@@ -0,0 +1,124 @@
+// Theme helper for landing page
+// Responsibilities:
+// - read/write `drawdb:theme` from localStorage (safely)
+// - apply `.theme-dark` or `.theme-light` class to document element
+// - provide toggle function
+// - listen to system preference changes and notify
+
+const STORAGE_KEY = "drawdb:theme";
+
+function safeGetStorage() {
+  try {
+    if (typeof window === "undefined" || !window.localStorage) return null;
+    return window.localStorage;
+  } catch (e) {
+    return null;
+  }
+}
+
+function getStoredTheme() {
+  const s = safeGetStorage();
+  try {
+    return s ? s.getItem(STORAGE_KEY) : null;
+  } catch (e) {
+    return null;
+  }
+}
+
+function setStoredTheme(value) {
+  const s = safeGetStorage();
+  try {
+    if (s) s.setItem(STORAGE_KEY, value);
+  } catch (e) {
+    // ignore storage errors (e.g., private mode)
+  }
+}
+
+function isSystemDark() {
+  try {
+    if (typeof window === "undefined" || !window.matchMedia) return true; // fallback to dark
+    return window.matchMedia("(prefers-color-scheme: dark)").matches;
+  } catch (e) {
+    return true;
+  }
+}
+
+function applyThemeClass(theme) {
+  try {
+    const root = document.documentElement || document.body;
+    if (!root) return;
+    root.classList.remove("theme-dark", "theme-light");
+    if (theme === "dark") root.classList.add("theme-dark");
+    else root.classList.add("theme-light");
+  } catch (e) {
+    // no-op
+  }
+}
+
+// Determine active theme: stored > system > default dark
+export function getTheme() {
+  const stored = getStoredTheme();
+  if (stored === "dark" || stored === "light") return stored;
+  const sys = isSystemDark() ? "dark" : "light";
+  return sys || "dark";
+}
+
+export function applyTheme(theme) {
+  applyThemeClass(theme);
+}
+
+// toggle and persist
+export function toggleTheme() {
+  const current = getTheme();
+  const next = current === "dark" ? "light" : "dark";
+  try {
+    setStoredTheme(next);
+  } catch (e) {
+    // ignore
+  }
+  applyThemeClass(next);
+  return next;
+}
+
+// Initialize on page load: apply stored or system preference, defaulting to dark
+export function initTheme() {
+  const stored = getStoredTheme();
+  const theme = stored === "dark" || stored === "light" ? stored : (isSystemDark() ? "dark" : "light");
+  applyThemeClass(theme);
+}
+
+// Listen to system preference changes and call callback(prefersDark)
+// Returns an unsubscribe function
+export function onSystemPrefChange(cb) {
+  try {
+    if (typeof window === "undefined" || !window.matchMedia) return () => {};
+    const mq = window.matchMedia("(prefers-color-scheme: dark)");
+    const handler = (ev) => cb(!!ev.matches);
+    // modern API
+    if (mq.addEventListener) mq.addEventListener("change", handler);
+    else mq.addListener && mq.addListener(handler);
+    return () => {
+      if (mq.removeEventListener) mq.removeEventListener("change", handler);
+      else mq.removeListener && mq.removeListener(handler);
+    };
+  } catch (e) {
+    return () => {};
+  }
+}
+
+// Auto-init if running in browser
+if (typeof window !== "undefined") {
+  try {
+    initTheme();
+  } catch (e) {
+    // ignore
+  }
+}
+
+export default {
+  getTheme,
+  applyTheme,
+  toggleTheme,
+  initTheme,
+  onSystemPrefChange,
+};