diff --git a/demo/Semi.Avalonia.Demo/Pages/NavigationPageDemo.axaml b/demo/Semi.Avalonia.Demo/Pages/NavigationPageDemo.axaml
index 00bf655..875aeee 100644
--- a/demo/Semi.Avalonia.Demo/Pages/NavigationPageDemo.axaml
+++ b/demo/Semi.Avalonia.Demo/Pages/NavigationPageDemo.axaml
@@ -61,6 +61,7 @@
                     <TextBlock Text="Modal Transition" FontWeight="SemiBold" FontSize="14" />
                     <ComboBox Name="TransitionCombo"
                               SelectedIndex="0"
+                              HorizontalAlignment="Stretch"
                               SelectionChanged="OnTransitionChanged">
                         <ComboBoxItem Content="Slide from Bottom" />
                         <ComboBoxItem Content="CrossFade" />