diff --git a/src/render.ts b/src/render.ts
index d5109b2..894d771 100644
--- a/src/render.ts
+++ b/src/render.ts
@@ -18,7 +18,9 @@ const icons = {
   download: `<svg viewBox="0 0 24 24" aria-hidden="true"><path d="M12 4v10m0 0 4-4m-4 4-4-4"/><path d="M5 18.5h14"/></svg>`,
   image: `<svg viewBox="0 0 24 24" aria-hidden="true"><rect x="4" y="5" width="16" height="14" rx="2"/><path d="m7 16 4-4 3 3 2-2 3 3"/><circle cx="8.5" cy="8.5" r="1.2"/></svg>`,
   share: `<svg viewBox="0 0 24 24" aria-hidden="true"><path d="M8.5 12.5 15.5 8.5M8.5 11.5 15.5 15.5"/><circle cx="6.5" cy="12" r="2.5"/><circle cx="17.5" cy="7.5" r="2.5"/><circle cx="17.5" cy="16.5" r="2.5"/></svg>`,
-  chevron: `<svg viewBox="0 0 24 24" aria-hidden="true"><path d="m8 10 4 4 4-4"/></svg>`
+  chevron: `<svg viewBox="0 0 24 24" aria-hidden="true"><path d="m8 10 4 4 4-4"/></svg>`,
+  sun: `<svg viewBox="0 0 24 24" aria-hidden="true"><circle cx="12" cy="12" r="4"/><path d="M12 3v2m0 14v2M3 12h2m14 0h2M5.6 5.6 7 7m10 10 1.4 1.4M18.4 5.6 17 7M7 17l-1.4 1.4"/></svg>`,
+  moon: `<svg viewBox="0 0 24 24" aria-hidden="true"><path d="M20 14.6A7.6 7.6 0 0 1 9.4 4 8 8 0 1 0 20 14.6Z"/></svg>`
 };
 
 function css(): string {
@@ -57,12 +59,19 @@ html[data-theme="dark"] {
   --bg: #212121; --panel: #212121; --text: #ececec; --muted: #a8a8a8; --border: #3f3f46; --soft: #2f2f2f; --code: #e5e7eb; --code-bg: #171717; --user-bubble: #303030;
 }
 * { box-sizing: border-box; }
+body, .topbar, .message.user .content, .content pre, .content :not(pre) > code, .code-block, .code-block .code-header, .content th, .content td, .content blockquote, .downloads, .icon-button, .shot-menu, .shot-menu button, .toast {
+  transition: background-color .22s ease, border-color .22s ease, color .22s ease, box-shadow .22s ease;
+}
 body { margin: 0; background: var(--bg); color: var(--text); font-size: 16px; line-height: 1.65; }
 a { color: inherit; }
 .page { min-height: 100vh; }
 .topbar { position: sticky; top: 0; z-index: 2; border-bottom: 1px solid var(--border); background: color-mix(in srgb, var(--bg) 92%, transparent); backdrop-filter: blur(12px); }
 .topbar-inner { max-width: 880px; margin: 0 auto; padding: 14px 20px; display: flex; align-items: center; justify-content: space-between; gap: 12px; }
+.topbar-actions { display: inline-flex; align-items: center; gap: 8px; min-width: 0; }
 .snapshot-label { font-size: 13px; color: var(--muted); white-space: nowrap; }
+.theme-toggle .moon-icon { display: none; }
+html[data-theme="dark"] .theme-toggle .sun-icon { display: none; }
+html[data-theme="dark"] .theme-toggle .moon-icon { display: block; }
 .title { max-width: 880px; margin: 0 auto; padding: 34px 20px 18px; }
 h1 { margin: 0; font-size: clamp(28px, 5vw, 44px); line-height: 1.12; letter-spacing: 0; }
 .conversation { max-width: 880px; margin: 0 auto; padding: 4px 20px 36px; }
@@ -125,6 +134,7 @@ h1 { margin: 0; font-size: clamp(28px, 5vw, 44px); line-height: 1.12; letter-spa
 @media (max-width: 640px) {
   body { font-size: 15px; }
   .topbar-inner { padding: 12px 16px; }
+  .topbar-actions { gap: 6px; }
   .title { padding: 26px 16px 12px; }
   .conversation { padding: 0 16px 28px; }
   .message { padding: 16px 0; }
@@ -137,17 +147,35 @@ h1 { margin: 0; font-size: clamp(28px, 5vw, 44px); line-height: 1.12; letter-spa
 }`;
 }
 
+function initialThemeScript(): string {
+  return `!function(){var p=new URLSearchParams(location.search),t=p.get("theme");if(t!=="light"&&t!=="dark")t=matchMedia("(prefers-color-scheme: dark)").matches?"dark":"light";document.documentElement.dataset.theme=t}();`;
+}
+
 function pageScript(slug: string): string {
   return `
 (function () {
   function currentVariant() {
     var device = matchMedia("(max-width: 640px)").matches ? "mobile" : "desktop";
-    var theme = matchMedia("(prefers-color-scheme: dark)").matches ? "dark" : "light";
+    var theme = document.documentElement.dataset.theme || (matchMedia("(prefers-color-scheme: dark)").matches ? "dark" : "light");
     return device + "-" + theme;
   }
   function downloadShot(variant) {
     location.href = "screenshots/" + variant + ".png";
   }
+  var systemTheme = matchMedia("(prefers-color-scheme: dark)");
+  var themeToggle = document.querySelector("[data-theme-toggle]");
+  var manualTheme = false;
+  function preferredTheme() {
+    return systemTheme.matches ? "dark" : "light";
+  }
+  function applyTheme(theme, manual) {
+    document.documentElement.dataset.theme = theme;
+    if (manual) manualTheme = true;
+    if (themeToggle) {
+      themeToggle.setAttribute("aria-label", theme === "dark" ? "Switch to light theme" : "Switch to dark theme");
+      themeToggle.setAttribute("title", theme === "dark" ? "Switch to light theme" : "Switch to dark theme");
+    }
+  }
   var toastTimer;
   function showToast(message) {
     var region = document.querySelector("[data-toast-region]");
@@ -176,7 +204,14 @@ function pageScript(slug: string): string {
   }
   var params = new URLSearchParams(location.search);
   var theme = params.get("theme");
-  if (theme === "light" || theme === "dark") document.documentElement.dataset.theme = theme;
+  manualTheme = theme === "light" || theme === "dark";
+  applyTheme(theme === "light" || theme === "dark" ? theme : preferredTheme(), theme === "light" || theme === "dark");
+  systemTheme.addEventListener("change", function () {
+    if (!manualTheme) applyTheme(preferredTheme(), false);
+  });
+  if (themeToggle) themeToggle.addEventListener("click", function () {
+    applyTheme(document.documentElement.dataset.theme === "dark" ? "light" : "dark", true);
+  });
   var copy = document.querySelector("[data-copy]");
   if (copy) copy.addEventListener("click", async function () {
     await copyText(location.href.replace(/[?#].*$/, ""), "Link copied");
@@ -229,11 +264,12 @@ export function renderConversationPage(slug: string, conversation: NormalizedCon
   <meta name="viewport" content="width=device-width, initial-scale=1">
   <meta name="robots" content="noindex">
   <title>${title}</title>
+  <script>${initialThemeScript()}</script>
   <style>${css()}</style>
 </head>
 <body>
   <div class="page">
-    <header class="topbar"><div class="topbar-inner"><strong>AI Share</strong><span class="snapshot-label">ChatGPT snapshot</span></div></header>
+    <header class="topbar"><div class="topbar-inner"><strong>AI Share</strong><div class="topbar-actions"><span class="snapshot-label">ChatGPT snapshot</span><button class="icon-button theme-toggle" type="button" data-theme-toggle aria-label="Switch theme" title="Switch theme"><span class="sun-icon">${icons.sun}</span><span class="moon-icon">${icons.moon}</span></button></div></div></header>
     <main>
       <section class="title"><h1>${title}</h1></section>
       <section class="conversation">${messages}</section>