Avalonia/src/Avalonia.Themes.Fluent/Controls/NavigationPage.xaml

<ResourceDictionary xmlns="https://github.com/avaloniaui"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
  <Design.PreviewWith>
    <Border Width="400" Height="600">
      <NavigationPage />
    </Border>
  </Design.PreviewWith>

  <StreamGeometry x:Key="NavigationPageMenuIcon">M3 17h18a1 1 0 0 1 .117 1.993L21 19H3a1 1 0 0 1-.117-1.993L3 17h18H3Zm0-6 18-.002a1 1 0 0 1 .117 1.993l-.117.007L3 13a1 1 0 0 1-.117-1.993L3 11l18-.002L3 11Zm0-6h18a1 1 0 0 1 .117 1.993L21 7H3a1 1 0 0 1-.117-1.993L3 5h18H3Z</StreamGeometry>

  <StreamGeometry x:Key="NavigationPageBackIcon">M12.7347,4.20949 C13.0332,3.92233 13.508,3.93153 13.7952,4.23005 C14.0823,4.52857 14.0731,5.00335 13.7746,5.29051 L5.50039,13.25 L24.2532,13.25 C24.6674,13.25 25.0032,13.5858 25.0032,13.9999982 C25.0032,14.4142 24.6674,14.75 24.2532,14.75 L5.50137,14.75 L13.7746,22.7085 C14.0731,22.9957 14.0823,23.4705 13.7952,23.769 C13.508,24.0675 13.0332,24.0767 12.7347,23.7896 L3.30673,14.7202 C2.89776,14.3268 2.89776,13.6723 3.30673,13.2788 L12.7347,4.20949 Z</StreamGeometry>

  <SolidColorBrush x:Key="NavigationBarBackground" Color="{DynamicResource SystemChromeMediumColor}" />
  <SolidColorBrush x:Key="NavigationBarForeground" Color="{DynamicResource SystemBaseMediumColor}" />

  <ControlTheme x:Key="{x:Type NavigationPage}" TargetType="NavigationPage">
    <!-- Transparent keeps the hit-test surface active for the back-swipe gesture edge area. -->
    <Setter Property="Background" Value="Transparent" />
    <Setter Property="PageTransition">
      <Setter.Value>
        <PageSlide Duration="0:0:0.3" Orientation="Horizontal" FillMode="Forward" />
      </Setter.Value>
    </Setter>
    <Setter Property="ModalTransition">
      <Setter.Value>
        <PageSlide Duration="0:0:0.25" Orientation="Vertical" FillMode="Forward" />
      </Setter.Value>
    </Setter>
    <Setter Property="Template">
      <ControlTemplate>
        <!-- ClipToBounds prevents slide animations bleeding outside the control bounds. -->
        <Panel ClipToBounds="True">
          <DockPanel>
            <!-- Reserves nav-bar height in Inset mode. Invisible in Overlay mode. -->
            <Border Name="PART_NavBarSpacer"
                    Height="{TemplateBinding EffectiveBarHeight}"
                    IsVisible="False"
                    DockPanel.Dock="Top" />

            <ContentPresenter Name="PART_BottomCommandBar"
                              DockPanel.Dock="Bottom"
                              HorizontalContentAlignment="Stretch"
                              Background="{TemplateBinding Background}"
                              Content="{Binding CurrentPage?.(NavigationPage.BottomCommandBar), RelativeSource={RelativeSource TemplatedParent}, FallbackValue={x:Null}}" />

            <!-- Back and front presenters enable slide transitions without Control recycling. -->
            <Grid Name="PART_ContentHost"
                  Background="{TemplateBinding Background}"
                  ClipToBounds="True">
              <ContentPresenter Name="PART_PageBackPresenter"
                                HorizontalAlignment="Stretch"
                                VerticalAlignment="Stretch" />
              <ContentPresenter Name="PART_PagePresenter"
                                HorizontalAlignment="Stretch"
                                VerticalAlignment="Stretch" />
            </Grid>
          </DockPanel>

          <!-- Navigation bar floats above content (ZIndex=1). -->
          <Border Name="PART_NavigationBar"
                  ZIndex="1"
                  VerticalAlignment="Top"
                  ClipToBounds="True"
                  Height="{TemplateBinding EffectiveBarHeight}">
            <Grid Margin="12,0,0,0" ColumnDefinitions="Auto, *, Auto">
              <Grid.Styles>
                <Style Selector="Button#PART_BackButton /template/ ContentPresenter#PART_ContentPresenter">
                  <Setter Property="Background" Value="Transparent" />
                  <Setter Property="CornerRadius" Value="4" />
                </Style>
                <Style Selector="Button#PART_BackButton:pointerover /template/ ContentPresenter#PART_ContentPresenter">
                  <Setter Property="Background" Value="{DynamicResource SubtleFillColorSecondaryBrush}" />
                </Style>
                <Style Selector="Button#PART_BackButton:pressed /template/ ContentPresenter#PART_ContentPresenter">
                  <Setter Property="Background" Value="{DynamicResource SubtleFillColorTertiaryBrush}" />
                </Style>
                <Style Selector="Button#PART_BackButton:disabled">
                  <Setter Property="Opacity" Value="0.4" />
                </Style>
                <Style Selector="Button#PART_BackButton:focus-visible /template/ ContentPresenter#PART_ContentPresenter">
                  <Setter Property="BorderBrush" Value="{DynamicResource SystemControlForegroundBaseHighBrush}" />
                  <Setter Property="BorderThickness" Value="2" />
                  <Setter Property="CornerRadius" Value="4" />
                </Style>
                <Style Selector="Button:disabled /template/ ContentPresenter#PART_ContentPresenter">
                  <Setter Property="Background" Value="Transparent" />
                </Style>
                <Style Selector="Button#PART_OverflowButton /template/ ContentPresenter#PART_ContentPresenter">
                  <Setter Property="Background" Value="Transparent" />
                  <Setter Property="CornerRadius" Value="0" />
                </Style>
                <Style Selector="Button#PART_OverflowButton:pointerover /template/ ContentPresenter#PART_ContentPresenter">
                  <Setter Property="Background" Value="{DynamicResource SubtleFillColorSecondaryBrush}" />
                </Style>
                <Style Selector="Button#PART_OverflowButton:pressed /template/ ContentPresenter#PART_ContentPresenter">
                  <Setter Property="Background" Value="{DynamicResource SubtleFillColorTertiaryBrush}" />
                </Style>
              </Grid.Styles>

              <Button x:Name="PART_BackButton"
                      Grid.Column="0"
                      Background="Transparent"
                      Foreground="{DynamicResource NavigationBarForeground}"
                      IsVisible="{TemplateBinding IsBackButtonEffectivelyVisible}"
                      VerticalAlignment="Stretch"
                      Padding="8,0"
                      ToolTip.Tip="{x:Null}">
                <Panel Background="Transparent">
                  <Path Data="{DynamicResource NavigationPageBackIcon}"
                        Fill="{DynamicResource NavigationBarForeground}"
                        Width="24"
                        Height="24"
                        Stretch="Uniform"
                        HorizontalAlignment="Center"
                        VerticalAlignment="Center"
                        IsVisible="{Binding CurrentPage?.(NavigationPage.BackButtonContent), RelativeSource={RelativeSource TemplatedParent}, Converter={x:Static ObjectConverters.IsNull}, FallbackValue=False}" />
                  <ContentPresenter
                    Content="{Binding CurrentPage?.(NavigationPage.BackButtonContent), RelativeSource={RelativeSource TemplatedParent}, FallbackValue={x:Null}}"
                    IsVisible="{Binding CurrentPage?.(NavigationPage.BackButtonContent), RelativeSource={RelativeSource TemplatedParent}, Converter={x:Static ObjectConverters.IsNotNull}, FallbackValue=False}"
                    VerticalAlignment="Center"
                    HorizontalAlignment="Center"/>
                </Panel>
              </Button>

              <ContentPresenter Name="PART_Header"
                                Grid.Column="1"
                                FontSize="20"
                                Foreground="{DynamicResource NavigationBarForeground}"
                                Content="{Binding CurrentPage?.Header, RelativeSource={RelativeSource TemplatedParent}, FallbackValue={x:Null}}"
                                VerticalAlignment="Center"
                                HorizontalAlignment="Stretch"
                                HorizontalContentAlignment="Stretch"
                                Margin="0,0,12,0" />

              <ContentPresenter Name="PART_TopCommandBar"
                                Grid.Column="2"
                                HorizontalAlignment="Right"
                                VerticalContentAlignment="Stretch"
                                Foreground="{DynamicResource NavigationBarForeground}"
                                Content="{Binding CurrentPage?.(NavigationPage.TopCommandBar), RelativeSource={RelativeSource TemplatedParent}, FallbackValue={x:Null}}">
                <ContentPresenter.Styles>
                  <Style Selector="CommandBar">
                    <Setter Property="Background" Value="Transparent" />
                    <Setter Property="MinHeight" Value="0" />
                    <Setter Property="Padding" Value="0" />
                    <Setter Property="VerticalAlignment" Value="Stretch" />
                  </Style>
                  <Style Selector="AppBarButton">
                    <Setter Property="MinHeight" Value="0" />
                    <Setter Property="Padding" Value="8,0" />
                  </Style>
                  <Style Selector="AppBarToggleButton">
                    <Setter Property="MinHeight" Value="0" />
                    <Setter Property="Padding" Value="8,0" />
                  </Style>
                  <Style Selector="Button#PART_OverflowButton">
                    <Setter Property="MinHeight" Value="0" />
                    <Setter Property="Padding" Value="8,0" />
                  </Style>
                </ContentPresenter.Styles>
              </ContentPresenter>
            </Grid>
          </Border>

          <!-- Nav-bar shadow gradient. Margin.Top is set from code to match EffectiveBarHeight. -->
          <Border Name="PART_NavBarShadow"
                  ZIndex="1"
                  VerticalAlignment="Top"
                  IsVisible="False"
                  Height="4"
                  IsHitTestVisible="False">
            <Border.Background>
              <LinearGradientBrush StartPoint="0%,0%" EndPoint="0%,100%">
                <GradientStop Color="#0C000000" Offset="0" />
                <GradientStop Color="#00000000" Offset="1" />
              </LinearGradientBrush>
            </Border.Background>
          </Border>

          <!-- Modal overlay: ZIndex=99 holds the static layer during transitions; ZIndex=100 is the animating modal. -->
          <ContentPresenter Name="PART_ModalBackPresenter"
                            ZIndex="99"
                            IsVisible="False"
                            Background="{TemplateBinding Background}" />
          <ContentPresenter Name="PART_ModalPresenter"
                            ZIndex="100"
                            IsVisible="False"
                            Background="{TemplateBinding Background}" />
        </Panel>
      </ControlTemplate>
    </Setter>

    <!-- Default nav bar background, overridable via a more-specific style selector -->
    <Style Selector="^ /template/ Border#PART_NavigationBar">
      <Setter Property="Background" Value="{DynamicResource NavigationBarBackground}" />
    </Style>

    <!-- :nav-bar-inset: spacer reserves nav-bar height so content is pushed below -->
    <Style Selector="^:nav-bar-inset /template/ Border#PART_NavBarSpacer">
      <Setter Property="IsVisible" Value="True" />
    </Style>

    <!-- :nav-bar-compact: collapse CommandBar labels when bar is too short -->
    <Style Selector="^:nav-bar-compact /template/ ContentPresenter#PART_TopCommandBar CommandBar">
      <Setter Property="DefaultLabelPosition" Value="Collapsed" />
    </Style>
  </ControlTheme>
</ResourceDictionary>