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

<ResourceDictionary
    xmlns="https://github.com/avaloniaui"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:u="https://irihi.tech/ursa">
    <ControlTheme x:Key="ToolBarExpandToggleButton" TargetType="ToggleButton">
        <Setter Property="Background" Value="Transparent" />
        <Setter Property="Template">
            <ControlTemplate>
                <ContentPresenter
                    x:Name="PART_ContentPresenter"
                    Padding="{TemplateBinding Padding}"
                    HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}"
                    VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}"
                    Background="{TemplateBinding Background}"
                    BorderBrush="{TemplateBinding BorderBrush}"
                    BorderThickness="{TemplateBinding BorderThickness}"
                    Content="{TemplateBinding Content}"
                    ContentTemplate="{TemplateBinding ContentTemplate}"
                    CornerRadius="{TemplateBinding CornerRadius}"
                    RecognizesAccessKey="True"
                    TextElement.FontSize="{TemplateBinding FontSize}"
                    TextElement.FontWeight="{TemplateBinding FontWeight}"
                    UseLayoutRounding="False" />
            </ControlTemplate>
        </Setter>
    </ControlTheme>
    <ControlTheme x:Key="{x:Type u:ToolBar}" TargetType="u:ToolBar">
        <Setter Property="HorizontalAlignment" Value="Left"/>
        <Setter Property="VerticalAlignment" Value="Top"/>
        <Setter Property="Background" Value="Transparent"/>
        <Setter Property="ItemsPanel">
            <ItemsPanelTemplate>
                <u:ToolBarPanel />
            </ItemsPanelTemplate>
        </Setter>
        <Setter Property="Template">
            <ControlTemplate TargetType="u:ToolBar">
                <Border
                    Name="PART_BackgroundBorder"
                    Padding="{TemplateBinding Padding}"
                    Background="{TemplateBinding Background}"
                    BorderBrush="{TemplateBinding BorderBrush}"
                    BorderThickness="{TemplateBinding BorderThickness}"
                    HorizontalAlignment="{TemplateBinding HorizontalAlignment}"
                    VerticalAlignment="{TemplateBinding VerticalAlignment}"
                    CornerRadius="4">
                    <DockPanel LastChildFill="True">
                        <ContentPresenter
                            Name="PART_Header"
                            Margin="8,0"
                            HorizontalAlignment="Left"
                            VerticalAlignment="Center"
                            Content="{TemplateBinding Header}"
                            ContentTemplate="{TemplateBinding HeaderTemplate}"
                            DockPanel.Dock="Left"
                            Foreground="{DynamicResource ToolBarHeaderForeground}"
                            IsVisible="{TemplateBinding Header,
                                                        Converter={x:Static ObjectConverters.IsNotNull}}" />
                        <Panel Name="PART_PopupButtonPanel" DockPanel.Dock="Right">
                            <ToggleButton
                                Name="button"
                                Padding="8,0"
                                VerticalAlignment="Stretch"
                                IsVisible="False"
                                Theme="{DynamicResource ToolBarExpandToggleButton}">
                                <PathIcon
                                    Name="PART_Icon"
                                    Height="12"
                                    Foreground="{DynamicResource ToolBarHeaderForeground}"
                                    Data="{DynamicResource ToolBarHorizontalMoreGlyph}" />
                            </ToggleButton>
                            <Popup
                                IsLightDismissEnabled="True"
                                IsOpen="{Binding #button.IsChecked, Mode=TwoWay}"
                                Placement="{TemplateBinding PopupPlacement}"
                                PlacementTarget="{Binding #button}">
                                <Border Padding="2" Theme="{DynamicResource CardBorder}">
                                    <StackPanel Name="{x:Static u:ToolBar.PART_OverflowPanel}" />
                                </Border>
                            </Popup>
                        </Panel>
                        <ItemsPresenter
                            HorizontalAlignment="Left"
                            VerticalAlignment="Center"
                            ItemsPanel="{TemplateBinding ItemsPanel}" />
                    </DockPanel>
                </Border>
            </ControlTemplate>
        </Setter>
        <Style Selector="^[Orientation=Horizontal]">
            <Setter Property="PopupPlacement" Value="BottomEdgeAlignedLeft" />
        </Style>
        <Style Selector="^[Orientation=Vertical]">
            <Setter Property="PopupPlacement" Value="RightEdgeAlignedTop" />
            <Style Selector="^ /template/ ContentPresenter#PART_Header">
                <Setter Property="DockPanel.Dock" Value="Top" />
                <Setter Property="HorizontalAlignment" Value="Center" />
                <Setter Property="VerticalAlignment" Value="Top" />
                <Setter Property="Margin" Value="0 8" />
            </Style>
            <Style Selector="^ /template/ Panel#PART_PopupButtonPanel">
                <Setter Property="DockPanel.Dock" Value="Bottom" />
            </Style>
            <Style Selector="^ /template/ ToggleButton#button">
                <Setter Property="Padding" Value="0 8" />
            </Style>
            <Style Selector="^ /template/ PathIcon#PART_Icon">
                <Setter Property="Data" Value="{DynamicResource ToolBarVerticalMoreGlyph}" />
                <Setter Property="Width" Value="12" />
                <Setter Property="Height" Value="{x:Static x:Double.NaN}" />
            </Style>
        </Style>
        <Style Selector="^:overflow /template/ ToggleButton#button">
            <Setter Property="IsVisible" Value="True" />
        </Style>
    </ControlTheme>

    <ControlTheme x:Key="{x:Type u:ToolBarSeparator}" TargetType="u:ToolBarSeparator">
        <Setter Property="Template">
            <ControlTemplate>
                <Rectangle
                    Name="PART_Rect"
                    Margin="4"
                    Fill="{DynamicResource ToolBarSeparatorForeground}" />
            </ControlTemplate>
        </Setter>
        <Style Selector="^ /template/ Rectangle#PART_Rect">
            <Setter Property="Width" Value="1" />
            <Setter Property="VerticalAlignment" Value="Stretch" />
            <Setter Property="HorizontalAlignment" Value="Center" />
        </Style>
        <Style Selector="^:vertical /template/ Rectangle#PART_Rect">
            <Setter Property="Height" Value="1" />
            <Setter Property="Width" Value="{x:Static x:Double.NaN}" />
            <Setter Property="HorizontalAlignment" Value="Stretch" />
            <Setter Property="VerticalAlignment" Value="Center" />
        </Style>
    </ControlTheme>
</ResourceDictionary>