Avalonia/samples/ControlCatalog/Pages/NavigationPage/NavigationPageModalTransitionsPage.xaml

<UserControl xmlns="https://github.com/avaloniaui"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             x:Class="ControlCatalog.Pages.NavigationPageModalTransitionsPage">
  <DockPanel>
    <ScrollViewer DockPanel.Dock="Right" Width="260">
      <StackPanel Margin="12" Spacing="8">
        <TextBlock Text="Configuration" FontSize="16" FontWeight="SemiBold"
                   Foreground="{DynamicResource SystemControlHighlightAccentBrush}" />

        <TextBlock Text="Modal Transition" />
        <ComboBox x:Name="TransitionCombo"
                  SelectedIndex="0"
                  HorizontalAlignment="Stretch"
                  SelectionChanged="OnTransitionChanged">
          <ComboBoxItem Content="Slide from Bottom" />
          <ComboBoxItem Content="Cross Fade" />
          <ComboBoxItem Content="None" />
        </ComboBox>

        <TextBlock Text="Duration (ms)" />
        <DockPanel>
          <TextBlock x:Name="DurationLabel" DockPanel.Dock="Right"
                     Text="300 ms"
                     FontSize="12" Opacity="0.7"
                     VerticalAlignment="Center"
                     Width="50" TextAlignment="Right" />
          <Slider x:Name="DurationSlider"
                  Minimum="100"
                  Maximum="1000"
                  Value="300"
                  TickFrequency="100"
                  IsSnapToTickEnabled="True"
                  ValueChanged="OnDurationChanged" />
        </DockPanel>

        <Separator />

        <Button Content="Open Modal"
                HorizontalAlignment="Stretch"
                Click="OnOpenModal" />
        <Button Content="Pop Modal"
                HorizontalAlignment="Stretch"
                Click="OnPopModal" />

        <TextBlock x:Name="StatusText"
                   Text="Modals: 0"
                   Opacity="0.7" />
      </StackPanel>
    </ScrollViewer>

    <Border DockPanel.Dock="Right" Width="1" Background="{DynamicResource SystemControlForegroundBaseMediumLowBrush}" />

    <Border Margin="12"
            BorderBrush="{DynamicResource SystemControlForegroundBaseMediumLowBrush}"
            BorderThickness="1"
            CornerRadius="6"
            ClipToBounds="True">
      <NavigationPage x:Name="DemoNav" />
    </Border>
  </DockPanel>
</UserControl>