diff --git a/app/views/active_admin/devise/sessions/new.html.erb b/app/views/active_admin/devise/sessions/new.html.erb
index efdb1f5..4e86b49 100644
--- a/app/views/active_admin/devise/sessions/new.html.erb
+++ b/app/views/active_admin/devise/sessions/new.html.erb
@@ -1,13 +1,29 @@
 <% if ActiveAdmin::Oidc.aa_v4? %>
   <div class="p-6 sm:p-8 space-y-4 md:space-y-6 w-full sm:max-w-md bg-white sm:rounded-md shadow dark:border dark:bg-gray-800/50 dark:border-gray-800">
-    <h2 class="text-xl font-bold text-gray-900 md:text-2xl dark:text-white flex gap-2 items-center">
-      <%= site_title %> <%= set_page_title t('active_admin.devise.login.title') %>
-    </h2>
+    <div class="flex gap-2 items-center">
+      <h2 class="text-xl font-bold text-gray-900 md:text-2xl dark:text-white flex gap-2 items-center">
+        <%= site_title %> <%= set_page_title t('active_admin.devise.login.title') %>
+      </h2>
+
+      <%# Active Admin's own dark mode toggle. The logged out layout renders
+          active_admin/html_head, which loads the JS that delegates clicks on
+          .dark-mode-toggle, so the button needs no script of its own. %>
+      <button type="button"
+              class="dark-mode-toggle ms-auto flex items-center w-9 h-9 justify-center text-gray-500 hover:text-gray-700 dark:text-gray-400 dark:hover:text-gray-200 text-sm"
+              aria-label="<%= t('active_admin.toggle_dark_mode', default: 'Toggle dark mode') %>">
+        <svg class="hidden dark:block w-5 h-5 rtl:-scale-x-100" aria-hidden="true" xmlns="http://www.w3.org/2000/svg" fill="none" viewBox="0 0 18 20"><path stroke="currentColor" stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M8.509 5.75c0-1.493.394-2.96 1.144-4.25h-.081a8.5 8.5 0 1 0 7.356 12.746A8.5 8.5 0 0 1 8.509 5.75Z"></path></svg>
+        <svg class="dark:hidden w-5 h-5" aria-hidden="true" xmlns="http://www.w3.org/2000/svg" fill="none" viewBox="0 0 20 20"><path stroke="currentColor" stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M10 3V1m0 18v-2M5.05 5.05 3.636 3.636m12.728 12.728L14.95 14.95M3 10H1m18 0h-2M5.05 14.95l-1.414 1.414M16.364 3.636 14.95 5.05M14 10a4 4 0 1 1-8 0 4 4 0 0 1 8 0Z"></path></svg>
+      </button>
+    </div>
 
     <% if ActiveAdmin::Oidc.config.stub_dev_env_login_enabled? %>
-      <p class="activeadmin-oidc-stub-login text-sm font-semibold border border-red-400 bg-red-50 text-red-900 rounded-md p-3 dark:bg-red-900/30 dark:border-red-700 dark:text-red-100">
+      <%# Classes copied from Active Admin's own error flash. The gem's views are
+          outside the host's Tailwind content path, so only utilities Active Admin
+          itself already emits are compiled. %>
+      <div class="activeadmin-oidc-stub-login flex items-center gap-3 p-4 rounded-lg bg-red-50 text-red-800 dark:bg-red-800 dark:text-red-300">
+        <svg class="w-5 h-5 shrink-0 text-red-400 dark:text-red-300" aria-hidden="true" xmlns="http://www.w3.org/2000/svg" fill="currentColor" viewBox="0 0 20 20"><path d="M10 .5a9.5 9.5 0 1 0 9.5 9.5A9.51 9.51 0 0 0 10 .5ZM10 15a1 1 0 1 1 0-2 1 1 0 0 1 0 2Zm1-4a1 1 0 0 1-2 0V6a1 1 0 0 1 2 0v5Z"/></svg>
         Stub login is enabled: the button below signs in without contacting the identity provider.
-      </p>
+      </div>
     <% end %>
 
     <%= button_to ActiveAdmin::Oidc.config.login_button_label,
diff --git a/lib/activeadmin/oidc/version.rb b/lib/activeadmin/oidc/version.rb
index 458ffdb..12e877b 100644
--- a/lib/activeadmin/oidc/version.rb
+++ b/lib/activeadmin/oidc/version.rb
@@ -2,6 +2,6 @@
 
 module ActiveAdmin
   module Oidc
-    VERSION = "2.2.0"
+    VERSION = "2.2.1"
   end
 end
diff --git a/lib/generators/active_admin/oidc/install/templates/sessions_new_v4.html.erb b/lib/generators/active_admin/oidc/install/templates/sessions_new_v4.html.erb
index 1d7832d..345d7d0 100644
--- a/lib/generators/active_admin/oidc/install/templates/sessions_new_v4.html.erb
+++ b/lib/generators/active_admin/oidc/install/templates/sessions_new_v4.html.erb
@@ -2,14 +2,30 @@
     route while ActiveAdmin::Oidc.config.stub_dev_env_login! is on,
     which only ever happens in the development environment. %>
 <div class="p-6 sm:p-8 space-y-4 md:space-y-6 w-full sm:max-w-md bg-white sm:rounded-md shadow dark:border dark:bg-gray-800/50 dark:border-gray-800">
-  <h2 class="text-xl font-bold text-gray-900 md:text-2xl dark:text-white flex gap-2 items-center">
-    <%= site_title %> <%= set_page_title t('active_admin.devise.login.title') %>
-  </h2>
+  <div class="flex gap-2 items-center">
+    <h2 class="text-xl font-bold text-gray-900 md:text-2xl dark:text-white flex gap-2 items-center">
+      <%= site_title %> <%= set_page_title t('active_admin.devise.login.title') %>
+    </h2>
+
+    <%# Active Admin's own dark mode toggle. The logged out layout renders
+        active_admin/html_head, which loads the JS that delegates clicks on
+        .dark-mode-toggle, so the button needs no script of its own. %>
+    <button type="button"
+            class="dark-mode-toggle ms-auto flex items-center w-9 h-9 justify-center text-gray-500 hover:text-gray-700 dark:text-gray-400 dark:hover:text-gray-200 text-sm"
+            aria-label="<%= t('active_admin.toggle_dark_mode', default: 'Toggle dark mode') %>">
+      <svg class="hidden dark:block w-5 h-5 rtl:-scale-x-100" aria-hidden="true" xmlns="http://www.w3.org/2000/svg" fill="none" viewBox="0 0 18 20"><path stroke="currentColor" stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M8.509 5.75c0-1.493.394-2.96 1.144-4.25h-.081a8.5 8.5 0 1 0 7.356 12.746A8.5 8.5 0 0 1 8.509 5.75Z"></path></svg>
+      <svg class="dark:hidden w-5 h-5" aria-hidden="true" xmlns="http://www.w3.org/2000/svg" fill="none" viewBox="0 0 20 20"><path stroke="currentColor" stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M10 3V1m0 18v-2M5.05 5.05 3.636 3.636m12.728 12.728L14.95 14.95M3 10H1m18 0h-2M5.05 14.95l-1.414 1.414M16.364 3.636 14.95 5.05M14 10a4 4 0 1 1-8 0 4 4 0 0 1 8 0Z"></path></svg>
+    </button>
+  </div>
 
   <% if ActiveAdmin::Oidc.config.stub_dev_env_login_enabled? %>
-    <p class="activeadmin-oidc-stub-login text-sm font-semibold border border-red-400 bg-red-50 text-red-900 rounded-md p-3 dark:bg-red-900/30 dark:border-red-700 dark:text-red-100">
+    <%# Classes copied from Active Admin's own error flash. The gem's views are
+        outside the host's Tailwind content path, so only utilities Active Admin
+        itself already emits are compiled. %>
+    <div class="activeadmin-oidc-stub-login flex items-center gap-3 p-4 rounded-lg bg-red-50 text-red-800 dark:bg-red-800 dark:text-red-300">
+      <svg class="w-5 h-5 shrink-0 text-red-400 dark:text-red-300" aria-hidden="true" xmlns="http://www.w3.org/2000/svg" fill="currentColor" viewBox="0 0 20 20"><path d="M10 .5a9.5 9.5 0 1 0 9.5 9.5A9.51 9.51 0 0 0 10 .5ZM10 15a1 1 0 1 1 0-2 1 1 0 0 1 0 2Zm1-4a1 1 0 0 1-2 0V6a1 1 0 0 1 2 0v5Z"/></svg>
       Stub login is enabled: the button below signs in without contacting the identity provider.
-    </p>
+    </div>
   <% end %>
 
   <%= button_to ActiveAdmin::Oidc.config.login_button_label,
diff --git a/spec/requests/login_page_spec.rb b/spec/requests/login_page_spec.rb
index fa01c7a..b47f879 100644
--- a/spec/requests/login_page_spec.rb
+++ b/spec/requests/login_page_spec.rb
@@ -38,6 +38,29 @@
     expect(response.body).to include(ActiveAdmin::Oidc::Configuration::DEFAULT_LOGIN_BUTTON_LABEL)
   end
 
+  # Active Admin renders its dark mode toggle only in the signed-in top
+  # bar, so the login page carries its own. The logged out layout already
+  # loads the JS that delegates clicks on `.dark-mode-toggle`, so the
+  # markup is the whole feature -- and losing it is silent.
+  describe "the dark mode toggle" do
+    it "renders on AA v4" do
+      skip "AA v3 has no dark mode" unless ActiveAdmin::Oidc.aa_v4?
+
+      get "/admin/login"
+
+      expect(response.body).to include("dark-mode-toggle")
+      expect(response.body).to match(/aria-label="[^"]+"[^>]*>/)
+    end
+
+    it "is not rendered on AA v3" do
+      skip "AA v4 branch renders the toggle" if ActiveAdmin::Oidc.aa_v4?
+
+      get "/admin/login"
+
+      expect(response.body).not_to include("dark-mode-toggle")
+    end
+  end
+
   # Regression: AA v3's formtastic stylesheet targets
   # `#login input[type="submit"]`, so a <button type="submit"> stays
   # unstyled (defaults to the dark browser/AA button). Switching to
diff --git a/spec/requests/stub_login_spec.rb b/spec/requests/stub_login_spec.rb
index a77038f..6b074ed 100644
--- a/spec/requests/stub_login_spec.rb
+++ b/spec/requests/stub_login_spec.rb
@@ -76,6 +76,27 @@ def enable_stub_login!(&claims_block)
       expect(response.body).not_to include(%(action="/admin/auth/oidc"))
       expect(response.body).to include(ActiveAdmin::Oidc.config.login_button_label)
     end
+
+    # Regression: the banner used to carry Tailwind colour utilities that
+    # no host ever compiled, because the gem's views sit outside the
+    # host's Tailwind content path -- it rendered white on white in dark
+    # mode. AA 4 reuses the classes AA's own error flash emits; AA 3 has
+    # no Tailwind and no dark mode, so it styles itself inline.
+    it "styles the warning with something the host's build actually has" do
+      enable_stub_login!
+
+      get "/admin/login"
+
+      if ActiveAdmin::Oidc.aa_v4?
+        expect(response.body).to match(
+          /class="activeadmin-oidc-stub-login[^"]*\bdark:bg-red-800\b/
+        )
+      else
+        expect(response.body).to match(
+          /class="activeadmin-oidc-stub-login"[^>]*style="[^"]*background:/
+        )
+      end
+    end
   end
 
   describe "POST /admin/login/stub" do