diff --git a/app/views/active_admin/devise/sessions/new.html.erb b/app/views/active_admin/devise/sessions/new.html.erb
index 7c49318..efe7aa0 100644
--- a/app/views/active_admin/devise/sessions/new.html.erb
+++ b/app/views/active_admin/devise/sessions/new.html.erb
@@ -15,10 +15,12 @@
   <div id="login">
     <h2><%= active_admin_application.site_title(self) %></h2>
 
-    <%= button_to ActiveAdmin::Oidc.config.login_button_label,
-                  "/admin/auth/oidc",
-                  method: :post,
-                  class: "activeadmin-oidc-login-button",
-                  data: { turbo: false } %>
+    <%= form_tag "/admin/auth/oidc",
+                 method: :post,
+                 class: "activeadmin-oidc-login-form formtastic",
+                 data: { turbo: false } do %>
+      <%= submit_tag ActiveAdmin::Oidc.config.login_button_label,
+                     class: "activeadmin-oidc-login-button" %>
+    <% end %>
   </div>
 <% end %>
diff --git a/lib/generators/active_admin/oidc/install/templates/sessions_new.html.erb b/lib/generators/active_admin/oidc/install/templates/sessions_new.html.erb
index e880bb6..0cd8d78 100644
--- a/lib/generators/active_admin/oidc/install/templates/sessions_new.html.erb
+++ b/lib/generators/active_admin/oidc/install/templates/sessions_new.html.erb
@@ -1,9 +1,11 @@
 <div id="login">
   <h2><%%= active_admin_application.site_title(self) %></h2>
 
-  <%%= button_to ActiveAdmin::Oidc.config.login_button_label,
-                "/admin/auth/oidc",
-                method: :post,
-                class: "activeadmin-oidc-login-button",
-                data: { turbo: false } %>
+  <%%= form_tag "/admin/auth/oidc",
+               method: :post,
+               class: "activeadmin-oidc-login-form formtastic",
+               data: { turbo: false } do %>
+    <%%= submit_tag ActiveAdmin::Oidc.config.login_button_label,
+                   class: "activeadmin-oidc-login-button" %>
+  <%% end %>
 </div>
diff --git a/spec/requests/login_page_spec.rb b/spec/requests/login_page_spec.rb
index fb34d07..fa01c7a 100644
--- a/spec/requests/login_page_spec.rb
+++ b/spec/requests/login_page_spec.rb
@@ -37,4 +37,18 @@
 
     expect(response.body).to include(ActiveAdmin::Oidc::Configuration::DEFAULT_LOGIN_BUTTON_LABEL)
   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
+  # button_to in the AA v3 branch silently regresses the themed blue
+  # SSO button to a dark default. Lock the v3 view to submit_tag.
+  it "renders the SSO button as an <input type=submit> on AA v3" do
+    skip "AA v4+ branch uses button_to with Tailwind classes" if ActiveAdmin::Oidc.aa_v4?
+
+    get "/admin/login"
+
+    expect(response.body).to match(/<input[^>]+type="submit"[^>]+value="[^"]*SSO[^"]*"/)
+    expect(response.body).not_to match(/<button[^>]+type="submit"/)
+  end
 end