diff --git a/src/PostIt.Tests/SessionStatusBannerTests.cs b/src/PostIt.Tests/SessionStatusBannerTests.cs
new file mode 100644
index 00000000..c1c569a8
--- /dev/null
+++ b/src/PostIt.Tests/SessionStatusBannerTests.cs
@@ -0,0 +1,122 @@
+using Avalonia.Controls;
+using Avalonia.Headless.XUnit;
+using Avalonia.VisualTree;
+using PostIt.ViewModels;
+using PostIt.Views;
+
+namespace PostIt.Tests;
+
+/// <summary>
+/// UI tests for <see cref="SessionStatusBanner"/>. Mounted inside
+/// a real <see cref="MainWindow"/> via the headless Avalonia
+/// platform declared in <c>TestApp.cs</c>.
+///
+/// <para>The pattern is the one that <c>UnitTest1.MainPage_Should_Load</c>
+/// established: a test attribute <c>[AvaloniaFact]</c> (from
+/// <c>Avalonia.Headless.XUnit</c>) instead of plain <c>[Fact]</c>,
+/// <c>new MainWindow()</c>, <c>window.Show()</c>. The AvaloniaFact
+/// attribute schedules the test body inside a dispatcher, which
+/// is the precondition for the headless Window's
+/// <c>PlatformManager.CreateWindow()</c> to find a registered
+/// service. A plain <c>[Fact]</c> test that calls
+/// <c>new Window().Show()</c> throws because the harness has not
+/// been initialised for that thread.</para>
+///
+/// <para>The session banner's <c>DataContext</c> is not wired in
+/// these tests: <c>App.OnFrameworkInitializationCompleted</c> is
+/// not called in a unit test, so we set the DataContext on the
+/// banner directly. The production code path is exercised
+/// end-to-end by the manual launch, not here.</para>
+/// </summary>
+public class SessionStatusBannerTests
+{
+    [AvaloniaFact]
+    public void Banner_renders_three_buttons_in_the_visual_tree()
+    {
+        var window = new MainWindow();
+        window.SessionBanner.DataContext = new SessionStatusViewModel();
+        window.Show();
+
+        var buttons = window.SessionBanner.GetVisualDescendants()
+            .OfType<Button>()
+            .ToList();
+
+        // Three buttons, named by their content text: Se
+        // déconnecter, Se connecter, Paramètres. If any one is
+        // missing, the user has no way to trigger the
+        // corresponding navigation event.
+        Assert.Equal(3, buttons.Count);
+        Assert.Contains(buttons, b => b.Content as string == "Se déconnecter");
+        Assert.Contains(buttons, b => b.Content as string == "Se connecter");
+        Assert.Contains(buttons, b => b.Content as string == "Paramètres");
+    }
+
+    [AvaloniaFact]
+    public void Banner_login_button_is_visible_when_logged_out()
+    {
+        var window = new MainWindow();
+        var vm = new SessionStatusViewModel();
+        Assert.True(vm.IsLoggedOut);  // VM default
+        window.SessionBanner.DataContext = vm;
+        window.Show();
+
+        var login = window.SessionBanner.GetVisualDescendants()
+            .OfType<Button>()
+            .Single(b => b.Content as string == "Se connecter");
+
+        // The XAML binds IsVisible to IsLoggedOut. After Show,
+        // the binding has been evaluated.
+        Assert.True(login.IsVisible);
+    }
+
+    [AvaloniaFact]
+    public void Banner_logout_button_is_hidden_when_logged_out()
+    {
+        var window = new MainWindow();
+        var vm = new SessionStatusViewModel();
+        Assert.False(vm.IsLoggedIn);  // VM default
+        window.SessionBanner.DataContext = vm;
+        window.Show();
+
+        var logout = window.SessionBanner.GetVisualDescendants()
+            .OfType<Button>()
+            .Single(b => b.Content as string == "Se déconnecter");
+
+        Assert.False(logout.IsVisible);
+    }
+
+    [AvaloniaFact]
+    public void Banner_settings_button_is_visible_regardless_of_session()
+    {
+        var window = new MainWindow();
+        window.SessionBanner.DataContext = new SessionStatusViewModel();
+        window.Show();
+
+        var settings = window.SessionBanner.GetVisualDescendants()
+            .OfType<Button>()
+            .Single(b => b.Content as string == "Paramètres");
+
+        // Paramètres is the only button with no IsVisible
+        // binding — always shown. The user's only path to the
+        // settings page goes through this button.
+        Assert.True(settings.IsVisible);
+    }
+
+    [AvaloniaFact]
+    public void Banner_session_label_reflects_DataContext()
+    {
+        var window = new MainWindow();
+        window.SessionBanner.DataContext = new SessionStatusViewModel();
+        window.Show();
+
+        var label = window.SessionBanner.GetVisualDescendants()
+            .OfType<TextBlock>()
+            .First(t => t.Text == "Déconnecté" || t.Text == "Connecté");
+
+        // Default SessionLabel is "Déconnecté" until Refresh()
+        // is called with a valid session. This pins the default
+        // so a future refactor that breaks the initial value
+        // (e.g. by removing the field initialiser) is caught.
+        Assert.Equal("Déconnecté", label.Text);
+    }
+}
diff --git a/src/PostIt/PostIt/App.axaml.cs b/src/PostIt/PostIt/App.axaml.cs
index a73096d2..ca7e051d 100644
--- a/src/PostIt/PostIt/App.axaml.cs
+++ b/src/PostIt/PostIt/App.axaml.cs
@@ -5,6 +5,7 @@ using Avalonia;
 using Avalonia.Controls;
 using Avalonia.Controls.ApplicationLifetimes;
 using Avalonia.Markup.Xaml;
+using Avalonia.Styling;
 using PostIt.Services;
 using PostIt.ViewModels;
 using PostIt.Views;
@@ -112,8 +113,24 @@ public partial class App : Application
         // DataContext, and the TwoWay bindings inside the page keep
         // mutating the same in-memory Settings instance that the rest
         // of the app reads (OidcClientOptions construction, etc.).
-        provider.GetRequiredService<SettingsPage>().DataContext =
-            provider.GetRequiredService<Settings>();
+        provider.GetRequiredService<SettingsPage>().DataContext = settings;
+
+        // Settings.DarkMode was previously a dead field: it round-
+        // tripped through the settings file and the SettingsPage
+        // CheckBox, but no consumer ever read it. Wire it here to
+        // Application.RequestedThemeVariant so the toggle takes
+        // effect immediately, and seed the initial theme from the
+        // value Load() just populated (so a dark-mode user lands on
+        // a dark window on first launch, not on a default-light
+        // window that flips after the user touches the toggle).
+        ApplyDarkMode(settings);
+        settings.PropertyChanged += (_, e) =>
+        {
+            if (e.PropertyName == nameof(Settings.DarkMode))
+            {
+                ApplyDarkMode(settings);
+            }
+        };
 
         if (ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktop)
         {
@@ -190,6 +207,12 @@ public partial class App : Application
         }
     }
 
+    private static void ApplyDarkMode(Settings settings)
+    {
+        Application.Current!.RequestedThemeVariant =
+                            settings.DarkMode ? ThemeVariant.Dark : ThemeVariant.Light;
+    }
+
     /// <summary>
     /// Run once after the main window is shown: try to refresh the
     /// cached OIDC tokens silently; on success, push MainPage on top
diff --git a/src/PostIt/PostIt/ViewModels/MainPageViewModel.cs b/src/PostIt/PostIt/ViewModels/MainPageViewModel.cs
index 74996bd9..a7c70ab3 100644
--- a/src/PostIt/PostIt/ViewModels/MainPageViewModel.cs
+++ b/src/PostIt/PostIt/ViewModels/MainPageViewModel.cs
@@ -2,7 +2,6 @@ using System;
 using System.Collections.ObjectModel;
 using System.Linq;
 using System.Threading.Tasks;
-using Avalonia.Styling;
 using CommunityToolkit.Mvvm.ComponentModel;
 using CommunityToolkit.Mvvm.Input;
 using PostIt.Models;
@@ -38,9 +37,6 @@ public partial class MainPageViewModel : ViewModelBase
     [ObservableProperty]
     public partial bool IsBusy { get; set; }
 
-    [ObservableProperty]
-    ThemeVariant themeVariant = ThemeVariant.Default;
-
     [ObservableProperty]
     public partial Settings Settings { get; private set; }