Shaker/Avalonia/SukiUI/Theme/TreeViewStyles.xaml

<Styles xmlns="https://github.com/avaloniaui"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:content="clr-namespace:SukiUI.Content"
        xmlns:theme="clr-namespace:SukiUI.Theme">
    <Design.PreviewWith>
        <Border Width="200"
                Padding="20"
                Background="{DynamicResource SukiBackground}">
            <TreeView>
                <TreeViewItem Header="blub">
                    <TreeViewItem Header="blub" />
                    <TreeViewItem Header="blub" />
                </TreeViewItem>
                <TreeViewItem Header="blub" />
                <TreeViewItem Header="blub" />
            </TreeView>
        </Border>
    </Design.PreviewWith>

    <Style Selector="TreeViewItem">
        <Setter Property="Template">
            <ControlTemplate>
                <StackPanel>
                    <Border Name="SelectionBorder"
                            Background="{TemplateBinding Background}"
                            BorderBrush="{TemplateBinding BorderBrush}"
                            BorderThickness="{TemplateBinding BorderThickness}"
                            CornerRadius="{TemplateBinding CornerRadius}"
                            Focusable="True"
                            TemplatedControl.IsTemplateFocusTarget="True">
                        <Grid Name="PART_Header"
                              Margin="{TemplateBinding Level,
                                                       Mode=OneWay,
                                                       Converter={StaticResource LeftMarginConverter}}"
                              ColumnDefinitions="16, *">
                            <Grid.Styles>
                                <Style Selector="ToggleButton:checked">
                                    <Setter Property="Background" Value="Transparent" />
                                </Style>
                            </Grid.Styles>
                            <ToggleButton Name="PART_ExpandCollapseChevron"
                                          Padding="0"
                                          Background="Transparent"
                                          BorderThickness="0"
                                          Classes="Basic"
                                          Focusable="False"
                                          RenderTransformOrigin="65% 50%" 
                                          IsChecked="{TemplateBinding IsExpanded,
                                                                      Mode=TwoWay}">
                                <ToggleButton.Transitions>
                                    <Transitions>
                                        <TransformOperationsTransition Property="RenderTransform" Duration="0.25" />
                                    </Transitions>
                                </ToggleButton.Transitions>
                                <PathIcon Width="7"
                                          Height="7"
                                          Classes="Flippable"
                                          Data="{x:Static content:Icons.ChevronRight}" />
                            </ToggleButton>
                            <ContentPresenter Name="PART_HeaderPresenter"
                                              Grid.Column="1"
                                              Padding="{TemplateBinding Padding}"
                                              HorizontalContentAlignment="{TemplateBinding HorizontalAlignment}"
                                              Background="Transparent"
                                              Content="{TemplateBinding Header}"
                                              ContentTemplate="{TemplateBinding HeaderTemplate}"
                                              Focusable="False" />
                        </Grid>
                    </Border>
                    <ItemsPresenter Name="PART_ItemsPresenter"
                                    theme:ItemsPresenterExtensions.AnimatedScroll="True"
                                    IsVisible="{TemplateBinding IsExpanded}"
                                    ItemsPanel="{TemplateBinding ItemsPanel}" />
                </StackPanel>
            </ControlTemplate>
        </Setter>
    </Style>

    <Style Selector="TreeViewItem">
        <Setter Property="CornerRadius" Value="{DynamicResource SmallCornerRadius}" />
        <Setter Property="Margin" Value="1" />
    </Style>
    <Style Selector="TreeView">
        <Setter Property="CornerRadius" Value="{DynamicResource SmallCornerRadius}" />
        <Setter Property="BorderThickness" Value="0" />
        <Setter Property="BorderBrush" Value="#dedede" />
        <Setter Property="Margin" Value="0" />
        <Setter Property="Padding" Value="0" />
    </Style>
    <Style Selector="TreeViewItem">
        <Setter Property="Padding" Value="5" />
    </Style>

    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    <Style Selector="TreeViewItem:pointerover /template/ Border#SelectionBorder:pointerover">
        <Setter Property="Background" Value="{DynamicResource SukiCardBackground}" />
    </Style>
    

    <Style Selector="TreeViewItem:selected /template/ Border#SelectionBorder:focus">
        <Setter Property="Background" Value="{DynamicResource SukiPrimaryColor}" />
    </Style>
   
    <Style Selector="TreeViewItem:selected /template/ Border#SelectionBorder:pointerover:focus">
        <Setter Property="Background" Value="{DynamicResource SukiPrimaryColor}" />
    </Style>
    


    <Style Selector="TreeViewItem:selected &gt; TextBlock">
        <Setter Property="Foreground" Value="{DynamicResource HighlightForegroundBrush}" />
    </Style>
    <!-- <Style Selector="TreeViewItem /template/ ToggleButton#expander"> -->
    <!--     <Setter Property="Background" Value="Transparent" /> -->
    <!--     <Setter Property="Padding" Value="0" /> -->
    <!--     <Setter Property="BorderThickness" Value="0" /> -->
    <!--     <Setter Property="Template"> -->
    <!--         <ControlTemplate> -->
    <!--  <Border Width="16"  -->
    <!--  Height="12"  -->
    <!--  HorizontalAlignment="Center"  -->
    <!--  VerticalAlignment="Center"  -->
    <!--  Background="Transparent"  -->
    <!--  BorderThickness="0">  -->
    <!--  <Path HorizontalAlignment="Center"  -->
    <!--  VerticalAlignment="Center"  -->
    <!--  Data="M 0 2 L 4 6 L 0 10 Z"  -->
    <!--  Fill="{DynamicResource ThemeForegroundBrush}" />  -->
    <!--             </Border> -->
    <!--         </ControlTemplate> -->
    <!--     </Setter> -->
    <!-- </Style> -->

    <Style Selector="TreeViewItem[IsExpanded=True] /template/ ToggleButton#PART_ExpandCollapseChevron">
        <Setter Property="RenderTransform" Value="rotate(90deg)" />
    </Style>
</Styles>