Shaker/Avalonia/SukiUI/Theme/TabControl.axaml

<ResourceDictionary xmlns="https://github.com/avaloniaui" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
    <ControlTheme x:Key="SukiTabControlStyle" TargetType="TabControl">
        <Setter Property="Margin" Value="0" />
        <Setter Property="Padding" Value="{DynamicResource TabItemMargin}" />
        <Setter Property="Background" Value="{DynamicResource TabControlBackground}" />
        <Setter Property="Template">
            <ControlTemplate>
                <Border HorizontalAlignment="{TemplateBinding HorizontalAlignment}"
                        VerticalAlignment="{TemplateBinding VerticalAlignment}"
                        Background="{TemplateBinding Background}"
                        BorderBrush="{TemplateBinding BorderBrush}"
                        BorderThickness="{TemplateBinding BorderThickness}"
                        CornerRadius="{TemplateBinding CornerRadius}">
                    <DockPanel>
                        <LayoutTransformControl Name="PART_LayoutTransform" DockPanel.Dock="{TemplateBinding TabStripPlacement}">
                            <ItemsPresenter Name="PART_ItemsPresenter" ItemsPanel="{TemplateBinding ItemsPanel}" />
                        </LayoutTransformControl>
                        <ContentPresenter Name="PART_SelectedContentHost"
                                          Margin="{TemplateBinding Padding}"
                                          HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}"
                                          VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}"
                                          Content="{TemplateBinding SelectedContent}"
                                          ContentTemplate="{TemplateBinding SelectedContentTemplate}" />
                    </DockPanel>
                </Border>
            </ControlTemplate>
        </Setter>

        <Style Selector="^[TabStripPlacement=Left] /template/ LayoutTransformControl#PART_LayoutTransform">
            <Setter Property="LayoutTransform" Value="rotate(-90deg)" />
            <Style Selector="^ ItemsPresenter#PART_ItemsPresenter WrapPanel">
                <Setter Property="Orientation" Value="Horizontal" />
                <Setter Property="FlowDirection" Value="{DynamicResource FlowDirectionOpposite}" />
            </Style>
        </Style>
        <Style Selector="^[TabStripPlacement=Right] /template/ LayoutTransformControl#PART_LayoutTransform">
            <Setter Property="LayoutTransform" Value="rotate(90deg)" />
            <Style Selector="^ ItemsPresenter#PART_ItemsPresenter WrapPanel">
                <Setter Property="Orientation" Value="Horizontal" />
            </Style>
        </Style>
        <Style Selector="^[TabStripPlacement=Top] /template/ ItemsPresenter#PART_ItemsPresenter">
            <Setter Property="Margin" Value="{DynamicResource TabControlTopPlacementItemMargin}" />
        </Style>
        
        <Style Selector="^.HorizontalTabs">
            <Style Selector="^[TabStripPlacement=Left] /template/ LayoutTransformControl#PART_LayoutTransform">
                <Setter Property="LayoutTransform" Value="rotate(0)" />
                <Style Selector="^ ItemsPresenter#PART_ItemsPresenter WrapPanel">
                    <Setter Property="Orientation" Value="Vertical" />
                    <Setter Property="FlowDirection" Value="{DynamicResource FlowDirectionOpposite}" />
                </Style>
            </Style>
            <Style Selector="^[TabStripPlacement=Right] /template/ LayoutTransformControl#PART_LayoutTransform">
                <Setter Property="LayoutTransform" Value="rotate(0)" />
                <Style Selector="^ ItemsPresenter#PART_ItemsPresenter WrapPanel">
                    <Setter Property="Orientation" Value="Vertical" />
                </Style>
            </Style>
        </Style>
    </ControlTheme>
    
    <ControlTheme x:Key="{x:Type TabControl}"
                  BasedOn="{StaticResource SukiTabControlStyle}"
                  TargetType="TabControl" />
</ResourceDictionary>