diff --git a/dsh/templates/chat.html b/dsh/templates/chat.html
index efcdc6a..7484efa 100644
--- a/dsh/templates/chat.html
+++ b/dsh/templates/chat.html
@@ -6,8 +6,16 @@
   <title>DeepSeek Harness — {{ DSH_USER }}</title>
   <link rel="stylesheet" href="/static/app.css">
   <style>
+    :root {
+      --canvas-soft: #f7f7f7; --surface: #ffffff; --surface-2: #f2f2f1; --hairline: #e6e6e6;
+      --ink: #111111; --ink-secondary: #333333; --ink-muted: #666666; --ink-faint: #999999; --primary: #0075de;
+    }
+    [data-theme="dark"] {
+      --canvas-soft: #141518; --surface: #1c1e22; --surface-2: #24262c; --hairline: #33363d;
+      --ink: #f5f6f7; --ink-secondary: #dcdee2; --ink-muted: #a9adb6; --ink-faint: #727680; --primary: #3d8be0;
+    }
     html, body { height: 100%; margin: 0; }
-    body { display: flex; flex-direction: column; }
+    body { display: flex; flex-direction: column; background: var(--surface, #fff); color: var(--ink, #111); }
     header.top { flex: none; }
     .app { display: flex; flex: 1; min-height: 0; }
     #sidebar {
@@ -15,7 +23,7 @@
       display: flex; flex-direction: column; background: var(--canvas-soft, #f7f7f7);
     }
     #sidebar h2 { font: 600 12px/1.3 var(--font-family, sans-serif); color: var(--ink-faint, #999); margin: 12px 12px 6px; }
-    #newBtn, #dlBtn { margin: 4px 12px; padding: 7px 10px; border: 1px solid #ddd; border-radius: 8px; background: #fff; cursor: pointer; text-align: left; }
+    #newBtn, #dlBtn { margin: 4px 12px; padding: 7px 10px; border: 1px solid var(--hairline, #e6e6e6); border-radius: 8px; background: #fff; cursor: pointer; text-align: left; }
     #sessions { list-style: none; margin: 0; padding: 0 8px; overflow: auto; flex: 1; }
     #sessions li {
       display: flex; align-items: center; gap: 6px; padding: 7px 8px; margin: 2px 0;
@@ -30,11 +38,11 @@
     .bubble { position: relative; white-space: pre-wrap; }
     .bubble .copy {
       position: absolute; top: 4px; right: 4px; display: none;
-      font-size: 11px; padding: 2px 6px; border: 1px solid #ddd; border-radius: 6px; background: #fff; cursor: pointer; color: #555;
+      font-size: 11px; padding: 2px 6px; border: 1px solid var(--hairline, #e6e6e6); border-radius: 6px; background: #fff; cursor: pointer; color: #555;
     }
     .msg:hover .bubble .copy { display: block; }
     .modelrow { display: flex; gap: 8px; align-items: center; }
-    .modelrow select { border: 1px solid #ddd; border-radius: 8px; padding: 6px 8px; font-size: 13px; }
+    .modelrow select { border: 1px solid var(--hairline, #e6e6e6); border-radius: 8px; padding: 6px 8px; font-size: 13px; }
   
   .modelrow label { font-size: 12px; color: #777; }
 
@@ -42,7 +50,7 @@
     .composer { display: flex; flex-direction: column; gap: 8px; padding: 8px 12px; }
     #input {
       width: 100%; min-height: 2.9em; padding: 9px 11px; box-sizing: border-box;
-      border: 1px solid #ddd; border-radius: 8px;
+      border: 1px solid var(--hairline, #e6e6e6); border-radius: 8px;
       font: 15px/1.4 var(--font-family, sans-serif); resize: vertical;
     }
     .send-row { display: flex; justify-content: flex-end; }
@@ -56,10 +64,10 @@
     #toolsBody { padding: 0 12px 10px; }
     #toolsBody.hidden { display: none; }
     .tools-row { display: flex; gap: 8px; flex-wrap: wrap; margin-top: 6px; }
-    .tools-row input[type=text], .tools-row input[type=file] { flex: 2 1 170px; border: 1px solid #ddd; border-radius: 8px; padding: 6px 10px; font-size: 13px; }
-    .tools-row button { flex: 0 0 auto; border: 1px solid #ddd; border-radius: 8px; padding: 6px 10px; cursor: pointer; background: #fff; }
+    .tools-row input[type=text], .tools-row input[type=file] { flex: 2 1 170px; border: 1px solid var(--hairline, #e6e6e6); border-radius: 8px; padding: 6px 10px; font-size: 13px; }
+    .tools-row button { flex: 0 0 auto; border: 1px solid var(--hairline, #e6e6e6); border-radius: 8px; padding: 6px 10px; cursor: pointer; background: #fff; }
     .modelrow { display: flex; gap: 8px; align-items: center; }
-    .modelrow select { border: 1px solid #ddd; border-radius: 8px; padding: 5px 8px; font-size: 13px; }
+    .modelrow select { border: 1px solid var(--hairline, #e6e6e6); border-radius: 8px; padding: 5px 8px; font-size: 13px; }
   @media (max-width: 720px) {
     #menuBtn { display: inline-flex !important; }
     #sidebar {
@@ -79,7 +87,8 @@
 </head>
 <body>
   <header class="top" style="display:flex;align-items:center;gap:8px;padding:10px 14px">
-    <button id="menuBtn" type="button" aria-label="Conversations" title="Conversations" style="display:none;align-items:center;justify-content:center;background:none;border:1px solid #ddd;border-radius:8px;padding:4px 9px;font-size:17px;cursor:pointer;line-height:1">☰</button>
+    <button id="menuBtn" type="button" aria-label="Conversations" title="Conversations" style="display:none;align-items:center;justify-content:center;background:none;border:1px solid var(--hairline, #e6e6e6);border-radius:8px;padding:4px 9px;font-size:17px;cursor:pointer;line-height:1">☰</button>
+    <button id="themeBtn" type="button" title="Toggle dark mode" style="background:none;border:1px solid var(--hairline, #e6e6e6);border-radius:8px;padding:4px 8px;font-size:16px;cursor:pointer;color:var(--ink, #111)">🌙</button>
     <div class="logo">DeepSeek Harness</div>
     <div class="who" style="margin-left:auto">{{ DSH_SLOT }} · <span class="model">{{ DSH_MODEL }}</span></div>
   </header>
@@ -301,6 +310,23 @@
     });
 
     fetchModels(); loadSessions();
+
+    // dark mode toggle (dsh standalone page)
+    (function () {
+      var root = document.documentElement;
+      var saved = null; try { saved = localStorage.getItem('dshTheme'); } catch(_) {}
+      if (saved === 'dark' || (!saved && window.matchMedia && window.matchMedia('(prefers-color-scheme: dark)').matches)) root.setAttribute('data-theme', 'dark');
+      var b = document.getElementById('themeBtn');
+      if (b) {
+        function sync(){ b.textContent = root.getAttribute('data-theme') === 'dark' ? '☀️' : '🌙'; }
+        b.addEventListener('click', function () {
+          if (root.getAttribute('data-theme') === 'dark') { root.removeAttribute('data-theme'); try{localStorage.setItem('dshTheme','light');}catch(_){} }
+          else { root.setAttribute('data-theme','dark'); try{localStorage.setItem('dshTheme','dark');}catch(_){} }
+          sync();
+        });
+        sync();
+      }
+    })();
   </script>
 </body>
 </html>
\ No newline at end of file
diff --git a/portal/static/app.css b/portal/static/app.css
index 410266d..54acb2d 100644
--- a/portal/static/app.css
+++ b/portal/static/app.css
@@ -71,7 +71,7 @@ a:hover { text-decoration: underline; }
   padding: 10px 12px;
   font: var(--type-body-sm);
   color: var(--ink);
-  border: 1px solid rgb(221, 221, 221);
+  border: 1px solid var(--hairline);
   border-radius: var(--rounded-xs);
   background: var(--surface);
 }
@@ -340,3 +340,8 @@ button.button, input[type="submit"].button { font-family: inherit; }
   .page { padding: var(--space-lg) var(--space-md); }
   .greeting { font: var(--type-heading-2); }
 }
+
+/* ---------- Dark-mode tweaks (hardcoded colours that need a dark variant) ---------- */
+[data-theme="dark"] .form-error { background: #3a2424; color: #ffb4ab; border-color: #7a4e4c; }
+[data-theme="dark"] .tool-icon { color: #1c1e22; }
+[data-theme="dark"] .category-pill { background: var(--surface-2); }
diff --git a/portal/static/tokens.css b/portal/static/tokens.css
index e037d62..0928910 100644
--- a/portal/static/tokens.css
+++ b/portal/static/tokens.css
@@ -14,6 +14,7 @@
   /* --- Surface --- */
   --canvas-soft: #f6f5f4;
   --surface: #ffffff;
+  --surface-2: #f2f2f1;
   --hairline: #e6e6e6;
 
   /* --- Text --- */
@@ -86,5 +87,23 @@
   --rounded-full: 9999px;
 }
 
+/* Dark mode — flip the semantic tokens only (components use var(--…)). */
+[data-theme="dark"] {
+  --canvas-soft: #141518;
+  --surface: #1c1e22;
+  --surface-2: #24262c;
+  --hairline: #33363d;
+  --ink: #f5f6f7;
+  --ink-secondary: #dcdee2;
+  --ink-muted: #a9adb6;
+  --ink-faint: #727680;
+  --primary: #3d8be0;
+  --primary-active: #5d9ff0;
+  --on-primary: #ffffff;
+  --secondary: #10142a;
+  --shadow-level-1: rgba(0, 0, 0, 0.45) 0 1px 3px;
+  --shadow-level-2: rgba(0, 0, 0, 0.55) 0 5px 22px;
+}
+
 /* Numerals: enable OpenType lnum */
 html { font-feature-settings: "lnum" 1; }
\ No newline at end of file
diff --git a/portal/templates/base.html b/portal/templates/base.html
index 4d37025..a345f6f 100644
--- a/portal/templates/base.html
+++ b/portal/templates/base.html
@@ -25,6 +25,7 @@
         <span>{{ user.full_name }}</span>
       </div>
       <a href="/account/password" class="button-utility" title="Change password">Password</a>
+      <button type="button" id="themeToggle" class="button-utility" title="Toggle dark mode" aria-label="Toggle dark mode">🌙</button>
       <a href="/logout" class="button-utility">Sign out</a>
     </div>
   </nav>
@@ -32,5 +33,25 @@
   <main>
   {% block content %}{% endblock %}
   </main>
+  <script>
+    (function () {
+      var root = document.documentElement;
+      var saved = null;
+      try { saved = localStorage.getItem('fhlTheme'); } catch (_) {}
+      var dark = saved === 'dark' || (!saved && window.matchMedia && window.matchMedia('(prefers-color-scheme: dark)').matches);
+      if (dark) root.setAttribute('data-theme', 'dark');
+      function sync() {
+        var b = document.getElementById('themeToggle');
+        if (b) b.textContent = root.getAttribute('data-theme') === 'dark' ? '☀️' : '🌙';
+      }
+      var t = document.getElementById('themeToggle');
+      if (t) t.addEventListener('click', function () {
+        if (root.getAttribute('data-theme') === 'dark') { root.removeAttribute('data-theme'); try { localStorage.setItem('fhlTheme','light'); } catch(_){} }
+        else { root.setAttribute('data-theme','dark'); try { localStorage.setItem('fhlTheme','dark'); } catch(_){} }
+        sync();
+      });
+      sync();
+    })();
+  </script>
 </body>
 </html>
\ No newline at end of file