diff --git a/src/Semi.Avalonia/Controls/Calendar.axaml b/src/Semi.Avalonia/Controls/Calendar.axaml
index 9381ce8..031181a 100644
--- a/src/Semi.Avalonia/Controls/Calendar.axaml
+++ b/src/Semi.Avalonia/Controls/Calendar.axaml
@@ -82,6 +82,7 @@
                                 Name="PART_HeaderButton"
                                 Grid.Column="1"
                                 HorizontalContentAlignment="Center"
+                                HorizontalAlignment="Stretch"
                                 Foreground="{TemplateBinding Foreground}"
                                 Theme="{DynamicResource BorderlessButton}" />