diff --git a/client/src/main.ts b/client/src/main.ts
index 7ef4b80..e223199 100644
--- a/client/src/main.ts
+++ b/client/src/main.ts
@@ -14,12 +14,54 @@ type Capture = {
 };
 
 const tokenKey = "aishare.adminToken";
+const themeKey = "aishare.adminTheme";
 const app = document.querySelector<HTMLDivElement>("#app")!;
 let token = localStorage.getItem(tokenKey) || "";
 let page = 1;
 let pageSize = 20;
+let totalPages = 1;
 let polling: number | undefined;
 let toastTimer: number | undefined;
+let manualTheme = false;
+
+const icons = {
+  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 preferredTheme() {
+  return window.matchMedia("(prefers-color-scheme: dark)").matches ? "dark" : "light";
+}
+
+function savedTheme() {
+  const theme = localStorage.getItem(themeKey);
+  return theme === "light" || theme === "dark" ? theme : null;
+}
+
+function applyTheme(theme: "light" | "dark", manual: boolean) {
+  document.documentElement.dataset.theme = theme;
+  document.documentElement.style.colorScheme = theme;
+  manualTheme = manual;
+  if (manual) localStorage.setItem(themeKey, theme);
+  updateThemeToggle();
+}
+
+function updateThemeToggle() {
+  const theme = document.documentElement.dataset.theme === "dark" ? "dark" : "light";
+  const toggle = document.querySelector<HTMLButtonElement>("[data-theme-toggle]");
+  if (!toggle) return;
+  toggle.setAttribute("aria-label", theme === "dark" ? "Switch to light theme" : "Switch to dark theme");
+  toggle.setAttribute("title", theme === "dark" ? "Switch to light theme" : "Switch to dark theme");
+}
+
+function initTheme() {
+  const theme = savedTheme();
+  applyTheme(theme || preferredTheme(), Boolean(theme));
+  const systemTheme = window.matchMedia("(prefers-color-scheme: dark)");
+  systemTheme.addEventListener("change", () => {
+    if (!manualTheme) applyTheme(preferredTheme(), false);
+  });
+}
 
 function serviceBaseUrl() {
   const url = new URL(location.href);
@@ -98,7 +140,10 @@ function renderShell() {
           <h1>AI Share Admin</h1>
           <p>Capture public ChatGPT shares as read-only snapshots.</p>
         </div>
-        <button class="icon-button" id="reset-token" title="Reset admin token" aria-label="Reset admin token">Reset</button>
+        <div class="header-actions">
+          <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>
+          <button class="icon-button" id="reset-token" title="Reset admin token" aria-label="Reset admin token">Reset</button>
+        </div>
       </header>
 
       <section class="panel token-panel" ${token ? "hidden" : ""}>
@@ -179,6 +224,11 @@ function renderShell() {
     renderShell();
   });
 
+  document.querySelector("[data-theme-toggle]")?.addEventListener("click", () => {
+    applyTheme(document.documentElement.dataset.theme === "dark" ? "light" : "dark", true);
+  });
+  updateThemeToggle();
+
   document.querySelector("#capture-form")?.addEventListener("submit", async (event) => {
     event.preventDefault();
     const form = event.currentTarget as HTMLFormElement;
@@ -227,6 +277,7 @@ function renderShell() {
     }
   });
   document.querySelector("#next")?.addEventListener("click", async () => {
+    if (page >= totalPages) return;
     page += 1;
     await loadCaptures();
   });
@@ -315,7 +366,7 @@ async function loadCaptures() {
   });
 
   const total = Number(body.total || 0);
-  const totalPages = Math.max(1, Math.ceil(total / pageSize));
+  totalPages = Math.max(1, Math.ceil(total / pageSize));
   if (page > totalPages) {
     page = totalPages;
     await loadCaptures();
@@ -350,5 +401,6 @@ function escapeHtml(value: string) {
     .replace(/"/g, "&quot;");
 }
 
+initTheme();
 renderShell();
 void loadCaptures();
diff --git a/client/src/styles.css b/client/src/styles.css
index c20577f..30e7f37 100644
--- a/client/src/styles.css
+++ b/client/src/styles.css
@@ -7,6 +7,9 @@
   --border: #d9dee7;
   --accent: #0f766e;
   --danger: #b42318;
+  --toast-bg: #ffffff;
+  --toast-text: #1f2328;
+  --shadow: rgb(15 23 42 / 14%);
   font-family: Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", "Noto Sans", Arial, sans-serif;
 }
 
@@ -19,14 +22,47 @@
     --border: #3f3f46;
     --accent: #14b8a6;
     --danger: #f87171;
+    --toast-bg: #2f2f33;
+    --toast-text: #f4f4f5;
+    --shadow: rgb(0 0 0 / 34%);
   }
 }
 
+html[data-theme="light"] {
+  color-scheme: light;
+  --bg: #f6f7f9;
+  --panel: #ffffff;
+  --text: #1f2328;
+  --muted: #6b7280;
+  --border: #d9dee7;
+  --accent: #0f766e;
+  --danger: #b42318;
+  --toast-bg: #ffffff;
+  --toast-text: #1f2328;
+  --shadow: rgb(15 23 42 / 14%);
+}
+
+html[data-theme="dark"] {
+  color-scheme: dark;
+  --bg: #18181b;
+  --panel: #242428;
+  --text: #f4f4f5;
+  --muted: #a1a1aa;
+  --border: #3f3f46;
+  --accent: #14b8a6;
+  --danger: #f87171;
+  --toast-bg: #2f2f33;
+  --toast-text: #f4f4f5;
+  --shadow: rgb(0 0 0 / 34%);
+}
+
 * { box-sizing: border-box; }
 body { margin: 0; background: var(--bg); color: var(--text); font-size: 15px; }
 button, input, select { font: inherit; }
+body, .panel, input, select, button, .small.link, .table-wrap, th, td, .pill { transition: background-color 180ms ease, border-color 180ms ease, color 180ms ease, box-shadow 180ms ease; }
 .shell { max-width: 1120px; margin: 0 auto; padding: 28px 20px 48px; }
 .header { display: flex; justify-content: space-between; gap: 20px; align-items: start; margin-bottom: 22px; }
+.header-actions { display: flex; align-items: center; gap: 8px; }
 h1, h2, p { margin: 0; }
 h1 { font-size: 30px; line-height: 1.15; letter-spacing: 0; }
 h2 { font-size: 18px; }
@@ -38,9 +74,15 @@ label { display: grid; gap: 6px; color: var(--muted); font-size: 13px; }
 input, select { min-height: 40px; border: 1px solid var(--border); border-radius: 7px; padding: 8px 10px; background: var(--panel); color: var(--text); }
 input { width: 100%; }
 button, .small.link { min-height: 38px; border: 1px solid var(--border); border-radius: 7px; padding: 8px 12px; background: var(--panel); color: var(--text); text-decoration: none; cursor: pointer; white-space: nowrap; }
+button:disabled { cursor: not-allowed; opacity: 0.42; }
 button[type="submit"] { background: var(--accent); border-color: var(--accent); color: white; }
 .danger { color: var(--danger); }
 .icon-button { min-height: 34px; }
+.theme-toggle { width: 38px; min-height: 38px; padding: 8px; display: inline-flex; align-items: center; justify-content: center; }
+.theme-toggle svg { width: 18px; height: 18px; fill: none; stroke: currentColor; stroke-width: 1.8; stroke-linecap: round; stroke-linejoin: round; }
+.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; }
 .table-head { justify-content: space-between; align-items: center; margin-bottom: 12px; }
 .table-wrap { overflow-x: auto; border: 1px solid var(--border); border-radius: 8px; }
 table { width: 100%; border-collapse: collapse; min-width: 760px; }
@@ -61,14 +103,16 @@ tr:last-child td { border-bottom: 0; }
 .pager-button { width: 38px; min-height: 36px; padding: 6px 10px; }
 .page-label { display: inline-flex; align-items: center; justify-content: center; min-width: 58px; font-variant-numeric: tabular-nums; color: var(--text); }
 .pager select { width: auto; min-height: 36px; padding: 6px 30px 6px 10px; }
-.toast { position: fixed; left: 50%; bottom: 22px; z-index: 50; transform: translate(-50%, 12px); padding: 9px 13px; border: 1px solid var(--border); border-radius: 8px; background: var(--text); color: var(--bg); box-shadow: 0 10px 28px rgb(0 0 0 / 18%); opacity: 0; pointer-events: none; transition: opacity 160ms ease, transform 160ms ease; }
+.toast { position: fixed; left: 50%; bottom: 22px; z-index: 50; transform: translate(-50%, 12px); padding: 9px 13px; border: 1px solid var(--border); border-radius: 8px; background: var(--toast-bg); color: var(--toast-text); box-shadow: 0 10px 28px var(--shadow); opacity: 0; pointer-events: none; transition: opacity 160ms ease, transform 160ms ease; }
 .toast[data-visible="true"] { opacity: 1; transform: translate(-50%, 0); }
 
 @media (max-width: 760px) {
   .shell { padding: 20px 14px 36px; }
   .header, .table-head, .actions { align-items: stretch; flex-direction: column; }
+  .header-actions { align-self: flex-end; }
   .capture-form { grid-template-columns: 1fr; }
   button { width: 100%; }
+  .theme-toggle { width: 38px; }
   .row-actions { justify-content: flex-start; flex-wrap: wrap; }
   .row-actions .small, .pager button, .pager select { width: auto; }
   .pager { flex-direction: row; justify-content: flex-end; align-items: center; }