默认情况下，选项卡项在选中时会隐藏其右边框。这会创建一个与选项卡内容混合的视觉外观。但是，由于您将选项卡项旋转了 90 度，因此它不再用于此目的。要获得正确的视觉反应，您需要编辑 TabItem 的 ControlTemplate。最简单的方法是从模板的副本开始（如果你有 Blend，你可以简单地去编辑模板副本）。如果您没有 Blend，那么您可以使用我的 Blend 版本创建的默认资源（如下）。然后编辑正确的边框属性以创建所需的视觉效果。
<Window.Resources>
<Style x:Key="TabItemFocusVisual">
<Setter Property="Control.Template">
<Setter.Value>
<ControlTemplate>
<Rectangle SnapsToDevicePixels="true" Margin="3,3,3,1" Stroke="Black" StrokeDashArray="1 2" StrokeThickness="1"/>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
<SolidColorBrush x:Key="TabControlNormalBorderBrush" Color="#8C8E94"/>
<LinearGradientBrush x:Key="ButtonNormalBackground" EndPoint="0,1" StartPoint="0,0">
<GradientStop Color="#F3F3F3" Offset="0"/>
<GradientStop Color="#EBEBEB" Offset="0.5"/>
<GradientStop Color="#DDDDDD" Offset="0.5"/>
<GradientStop Color="#CDCDCD" Offset="1"/>
</LinearGradientBrush>
<LinearGradientBrush x:Key="TabItemHotBackground" EndPoint="0,1" StartPoint="0,0">
<GradientStop Color="#EAF6FD" Offset="0.15"/>
<GradientStop Color="#D9F0FC" Offset=".5"/>
<GradientStop Color="#BEE6FD" Offset=".5"/>
<GradientStop Color="#A7D9F5" Offset="1"/>
</LinearGradientBrush>
<SolidColorBrush x:Key="TabItemSelectedBackground" Color="#F9F9F9"/>
<SolidColorBrush x:Key="TabItemHotBorderBrush" Color="#3C7FB1"/>
<SolidColorBrush x:Key="TabItemDisabledBackground" Color="#F4F4F4"/>
<SolidColorBrush x:Key="TabItemDisabledBorderBrush" Color="#FFC9C7BA"/>
<Style x:Key="TabItemStyle1" TargetType="{x:Type TabItem}">
<Setter Property="FocusVisualStyle" Value="{StaticResource TabItemFocusVisual}"/>
<Setter Property="Foreground" Value="Black"/>
<Setter Property="Padding" Value="6,1,6,1"/>
<Setter Property="BorderBrush" Value="{StaticResource TabControlNormalBorderBrush}"/>
<Setter Property="Background" Value="{StaticResource ButtonNormalBackground}"/>
<Setter Property="HorizontalContentAlignment" Value="Stretch"/>
<Setter Property="VerticalContentAlignment" Value="Stretch"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type TabItem}">
<Grid SnapsToDevicePixels="true">
<Border x:Name="Bd" Background="{TemplateBinding Background}" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="1,1,1,0" Padding="{TemplateBinding Padding}">
<ContentPresenter SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" HorizontalAlignment="{Binding Path=HorizontalContentAlignment, RelativeSource={RelativeSource AncestorType={x:Type ItemsControl}}}" x:Name="Content" VerticalAlignment="{Binding Path=VerticalContentAlignment, RelativeSource={RelativeSource AncestorType={x:Type ItemsControl}}}" ContentSource="Header" RecognizesAccessKey="True"/>
</Border>
</Grid>
<ControlTemplate.Triggers>
<Trigger Property="IsMouseOver" Value="true">
<Setter Property="Background" TargetName="Bd" Value="{StaticResource TabItemHotBackground}"/>
</Trigger>
<Trigger Property="IsSelected" Value="true">
<Setter Property="Panel.ZIndex" Value="1"/>
<Setter Property="Background" TargetName="Bd" Value="{StaticResource TabItemSelectedBackground}"/>
</Trigger>
<MultiTrigger>
<MultiTrigger.Conditions>
<Condition Property="IsSelected" Value="false"/>
<Condition Property="IsMouseOver" Value="true"/>
</MultiTrigger.Conditions>
<Setter Property="BorderBrush" TargetName="Bd" Value="{StaticResource TabItemHotBorderBrush}"/>
</MultiTrigger>
<Trigger Property="TabStripPlacement" Value="Bottom">
<Setter Property="BorderThickness" TargetName="Bd" Value="1,0,1,1"/>
</Trigger>
<Trigger Property="TabStripPlacement" Value="Left">
<Setter Property="BorderThickness" TargetName="Bd" Value="1,1,0,1"/>
</Trigger>
<Trigger Property="TabStripPlacement" Value="Right">
<Setter Property="BorderThickness" TargetName="Bd" Value="0,1,1,1"/>
</Trigger>
<MultiTrigger>
<MultiTrigger.Conditions>
<Condition Property="IsSelected" Value="true"/>
<Condition Property="TabStripPlacement" Value="Top"/>
</MultiTrigger.Conditions>
<Setter Property="Margin" Value="-2,-2,-2,-1"/>
<Setter Property="Margin" TargetName="Content" Value="0,0,0,1"/>
</MultiTrigger>
<MultiTrigger>
<MultiTrigger.Conditions>
<Condition Property="IsSelected" Value="true"/>
<Condition Property="TabStripPlacement" Value="Bottom"/>
</MultiTrigger.Conditions>
<Setter Property="Margin" Value="-2,-1,-2,-2"/>
<Setter Property="Margin" TargetName="Content" Value="0,1,0,0"/>
</MultiTrigger>
<MultiTrigger>
<MultiTrigger.Conditions>
<Condition Property="IsSelected" Value="true"/>
<Condition Property="TabStripPlacement" Value="Left"/>
</MultiTrigger.Conditions>
<Setter Property="Margin" Value="-2,-2,-1,-2"/>
<Setter Property="Margin" TargetName="Content" Value="0,0,1,0"/>
</MultiTrigger>
<MultiTrigger>
<MultiTrigger.Conditions>
<Condition Property="IsSelected" Value="true"/>
<Condition Property="TabStripPlacement" Value="Right"/>
</MultiTrigger.Conditions>
<Setter Property="Margin" Value="-1,-2,-2,-2"/>
<Setter Property="Margin" TargetName="Content" Value="1,0,0,0"/>
</MultiTrigger>
<Trigger Property="IsEnabled" Value="false">
<Setter Property="Background" TargetName="Bd" Value="{StaticResource TabItemDisabledBackground}"/>
<Setter Property="BorderBrush" TargetName="Bd" Value="{StaticResource TabItemDisabledBorderBrush}"/>
<Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</Window.Resources>