Ursa.Avalonia/src/Ursa.Themes.Semi/Controls/PathPicker.axaml

<ResourceDictionary
    xmlns="https://github.com/avaloniaui"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:converters="clr-namespace:Ursa.Themes.Semi.Converters"
    xmlns:u="https://irihi.tech/ursa">
    <Design.PreviewWith>
        <StackPanel Margin="20">
            <u:PathPicker Title="Hello World" Width="300" />
        </StackPanel>
    </Design.PreviewWith>
    <ControlTheme x:Key="{x:Type u:PathPicker}" TargetType="u:PathPicker">
        <Setter Property="CornerRadius" Value="3" />
        <Setter Property="Template">
            <ControlTemplate>
                <DockPanel>
                    <Button
                        Name="{x:Static u:PathPicker.PART_Button}"
                        HorizontalAlignment="Stretch"
                        VerticalAlignment="Center"
                        Content="{TemplateBinding Title}"
                        DockPanel.Dock="Right" />
                    <TextBox
                        Name="PART_TextBox"
                        AcceptsReturn="{TemplateBinding AllowMultiple}"
                        DockPanel.Dock="Left"
                        Text="{TemplateBinding SelectedPathsText,
                                               Mode=TwoWay}" />
                </DockPanel>
            </ControlTemplate>
        </Setter>

        <Style Selector="^ /template/ Button#PART_Button:pressed">
            <Setter Property="RenderTransform" Value="{x:Null}" />
        </Style>

        <Style Selector="^ /template/ Button#PART_Button">
            <Setter Property="DockPanel.Dock" Value="Right" />
            <Setter Property="VerticalAlignment" Value="Center" />
            <Setter Property="CornerRadius" Value="{TemplateBinding CornerRadius, Converter={x:Static converters:CornerRadiusTakeConverter.Right}}" />
            <Setter Property="Margin" Value="1 0 0 0" />
        </Style>
        <Style Selector="^ /template/ TextBox#PART_TextBox">
            <Setter Property="DockPanel.Dock" Value="Left" />
            <Setter Property="CornerRadius" Value="{TemplateBinding CornerRadius, Converter={x:Static converters:CornerRadiusTakeConverter.Left}}" />
        </Style>
        <Style Selector="^.Top">
            <Style Selector="^ /template/ Button#PART_Button">
                <Setter Property="DockPanel.Dock" Value="Top" />
                <Setter Property="CornerRadius" Value="{TemplateBinding CornerRadius, Converter={x:Static converters:CornerRadiusTakeConverter.Top}}" />
                <Setter Property="Margin" Value="0 0 0 1" />
            </Style>
            <Style Selector="^ /template/ TextBox#PART_TextBox">
                <Setter Property="DockPanel.Dock" Value="Bottom" />
                <Setter Property="CornerRadius" Value="{TemplateBinding CornerRadius, Converter={x:Static converters:CornerRadiusTakeConverter.Bottom}}" />
            </Style>
        </Style>
    </ControlTheme>


    <ControlTheme x:Key="ButtonPathPicker" TargetType="u:PathPicker">
        <Setter Property="Template">
            <ControlTemplate>
                <Button
                    Name="{x:Static u:PathPicker.PART_Button}"
                    HorizontalAlignment="{TemplateBinding HorizontalAlignment}"
                    VerticalAlignment="{TemplateBinding VerticalAlignment}"
                    Content="{TemplateBinding Title}" />
            </ControlTemplate>
        </Setter>
        <Style Selector="^ /template/ Button#PART_Button:pressed">
            <Setter Property="RenderTransform" Value="{x:Null}" />
        </Style>
    </ControlTheme>

    <ControlTheme x:Key="ListPathPicker" TargetType="u:PathPicker">
        <Setter Property="CornerRadius" Value="3" />
        <Setter Property="Template">
            <ControlTemplate>
                <Expander
                    HorizontalAlignment="{TemplateBinding HorizontalAlignment}"
                    VerticalAlignment="{TemplateBinding VerticalAlignment}"
                    CornerRadius="{TemplateBinding CornerRadius}"
                    Theme="{StaticResource INTERNAL_PathPickerExpander}">
                    <Expander.Header>
                        <Button
                            Name="PART_Button"
                            HorizontalAlignment="Stretch"
                            Content="{TemplateBinding Title}"
                            CornerRadius="{TemplateBinding CornerRadius,
                                                           Converter={x:Static converters:CornerRadiusTakeConverter.Left}}" />
                    </Expander.Header>
                    <ListBox ItemsSource="{TemplateBinding SelectedPaths}" />
                </Expander>
            </ControlTemplate>
        </Setter>
        <Style Selector="^ /template/ Button#PART_Button:pressed">
            <Setter Property="RenderTransform" Value="{x:Null}" />
        </Style>
    </ControlTheme>

    <ControlTheme x:Key="INTERNAL_PathPickerExpander" TargetType="Expander">
        <Setter Property="Template">
            <ControlTemplate>
                <DockPanel>
                    <DockPanel DockPanel.Dock="Top" LastChildFill="True">
                        <ToggleButton
                            Name="ExpanderHeader"
                            Margin="1,0,0,0"
                            Background="{DynamicResource ToggleButtonDefaultBackground}"
                            CornerRadius="{TemplateBinding CornerRadius,
                                                           Converter={x:Static converters:CornerRadiusTakeConverter.Right}}"
                            DockPanel.Dock="Right"
                            IsChecked="{TemplateBinding IsExpanded,
                                                        Mode=TwoWay}"
                            Theme="{DynamicResource INTERNAL_PathPickerExpanderHeaderToggleButtonTheme}">
                            <PathIcon
                                Name="PART_PathIcon"
                                Data="{DynamicResource ExpanderIcon}"
                                Theme="{DynamicResource InnerPathIcon}">
                                <PathIcon.Transitions>
                                    <Transitions>
                                        <TransformOperationsTransition Property="RenderTransform" Duration="0.1" />
                                    </Transitions>
                                </PathIcon.Transitions>
                            </PathIcon>
                        </ToggleButton>
                        <ContentPresenter Content="{TemplateBinding Header}" ContentTemplate="{TemplateBinding HeaderTemplate}" />
                    </DockPanel>
                    <ContentPresenter
                        Name="PART_ContentPresenter"
                        Margin="{DynamicResource ExpanderContentMargin}"
                        HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}"
                        VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}"
                        Content="{TemplateBinding Content}"
                        ContentTemplate="{TemplateBinding ContentTemplate}"
                        Foreground="{DynamicResource ExpanderContentForeground}"
                        IsVisible="{TemplateBinding IsExpanded,
                                                    Mode=TwoWay}" />
                </DockPanel>
            </ControlTemplate>
        </Setter>

        <Style Selector="^:expanded /template/ PathIcon#PART_PathIcon">
            <Setter Property="RenderTransform" Value="rotate(180deg)" />
        </Style>

    </ControlTheme>

    <ControlTheme x:Key="INTERNAL_PathPickerExpanderHeaderToggleButtonTheme" TargetType="ToggleButton">
        <Setter Property="Padding" Value="{DynamicResource ButtonDefaultPadding}" />
        <Setter Property="Cursor" Value="Hand" />
        <Setter Property="Template">
            <ControlTemplate TargetType="ToggleButton">
                <ContentPresenter
                    Padding="{TemplateBinding Padding}"
                    Background="{TemplateBinding Background}"
                    Content="{TemplateBinding Content}"
                    CornerRadius="{TemplateBinding CornerRadius}" />
            </ControlTemplate>
        </Setter>
    </ControlTheme>
</ResourceDictionary>