Update MainWindow.axaml

src/TypefaceUtil.Avalonia/Views/MainWindow.axaml

@@ -36,6 +36,7 @@
     </Panel.Styles>
 
     <StackPanel MaxWidth="640" 
+                MinWidth="640"
                 HorizontalAlignment="Center" 
                 VerticalAlignment="Center"
                 IsVisible="{Binding Typeface, Converter={x:Static ObjectConverters.IsNull}}">