白线是Popup 模板的一部分，这是MenuItem 在其默认模板中使用的。您必须覆盖它才能删除这些衬里。
如果您有Blend，那么您可以轻松更改模板并将代码复制粘贴到您的项目中。如果您没有 Blend，请试一试：
1- 添加对PresentationFramework.Aero的引用
2- 在您的 XAML 文件中，导入此命名空间：
xmlns:Themes="clr-namespace:Microsoft.Windows.Themes;assembly=PresentationFramework.Aero"
将此代码粘贴到Window.Resources 部分。这是 Blend 基于修改后的模板生成的：
<LinearGradientBrush x:Key="MenuItemSelectionFill" EndPoint="0,1" StartPoint="0,0">
<GradientStop Color="#34C5EBFF" Offset="0"/>
<GradientStop Color="#3481D8FF" Offset="1"/>
</LinearGradientBrush>
<Geometry x:Key="Checkmark">M 0,5.1 L 1.7,5.2 L 3.4,7.1 L 8,0.4 L 9.2,0 L 3.3,10.8 Z</Geometry>
<ControlTemplate x:Key="{ComponentResourceKey ResourceId=SubmenuItemTemplateKey, TypeInTargetAssembly={x:Type MenuItem}}" TargetType="{x:Type MenuItem}">
<Grid SnapsToDevicePixels="true">
<Rectangle x:Name="Bg" Fill="{TemplateBinding Background}" RadiusY="2" RadiusX="2" Stroke="{TemplateBinding BorderBrush}" StrokeThickness="1"/>
<Rectangle x:Name="InnerBorder" Margin="1" RadiusY="2" RadiusX="2"/>
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition MinWidth="24" SharedSizeGroup="MenuItemIconColumnGroup" Width="Auto"/>
<ColumnDefinition Width="4"/>
<ColumnDefinition Width="*"/>
<ColumnDefinition Width="37"/>
<ColumnDefinition SharedSizeGroup="MenuItemIGTColumnGroup" Width="Auto"/>
<ColumnDefinition Width="17"/>
</Grid.ColumnDefinitions>
<ContentPresenter x:Name="Icon" ContentSource="Icon" Margin="1" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" VerticalAlignment="Center"/>
<Border x:Name="GlyphPanel" BorderBrush="#CDD3E6" BorderThickness="1" Background="#E6EFF4" CornerRadius="3" Height="22" Margin="1" Visibility="Hidden" Width="22">
<Path x:Name="Glyph" Data="{StaticResource Checkmark}" Fill="#0C12A1" FlowDirection="LeftToRight" Height="11" Width="9"/>
</Border>
<ContentPresenter Grid.Column="2" ContentSource="Header" Margin="{TemplateBinding Padding}" RecognizesAccessKey="True" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
<TextBlock Grid.Column="4" Margin="{TemplateBinding Padding}" Text="{TemplateBinding InputGestureText}"/>
</Grid>
</Grid>
<ControlTemplate.Triggers>
<Trigger Property="Icon" Value="{x:Null}">
<Setter Property="Visibility" TargetName="Icon" Value="Collapsed"/>
</Trigger>
<Trigger Property="IsChecked" Value="true">
<Setter Property="Visibility" TargetName="GlyphPanel" Value="Visible"/>
<Setter Property="Visibility" TargetName="Icon" Value="Collapsed"/>
</Trigger>
<Trigger Property="IsHighlighted" Value="true">
<Setter Property="Fill" TargetName="Bg" Value="{StaticResource MenuItemSelectionFill}"/>
<Setter Property="Stroke" TargetName="Bg" Value="#8071CBF1"/>
<Setter Property="Stroke" TargetName="InnerBorder" Value="#40FFFFFF"/>
</Trigger>
<Trigger Property="IsEnabled" Value="false">
<Setter Property="Foreground" Value="#FF9A9A9A"/>
<Setter Property="Background" TargetName="GlyphPanel" Value="#EEE9E9"/>
<Setter Property="BorderBrush" TargetName="GlyphPanel" Value="#DBD6D6"/>
<Setter Property="Fill" TargetName="Glyph" Value="#848589"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
<LinearGradientBrush x:Key="MenuItemPressedFill" EndPoint="0,1" StartPoint="0,0">
<GradientStop Color="#28717070" Offset="0"/>
<GradientStop Color="#50717070" Offset="0.75"/>
<GradientStop Color="#90717070" Offset="1"/>
</LinearGradientBrush>
<Geometry x:Key="UpArrow">M 0,4 L 3.5,0 L 7,4 Z</Geometry>
<Style x:Key="MenuScrollButton" BasedOn="{x:Null}" TargetType="{x:Type RepeatButton}">
<Setter Property="ClickMode" Value="Hover"/>
<Setter Property="MinWidth" Value="0"/>
<Setter Property="MinHeight" Value="0"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type RepeatButton}">
<DockPanel Background="Transparent" SnapsToDevicePixels="true">
<Rectangle x:Name="R1" DockPanel.Dock="Right" Fill="Transparent" Width="1"/>
<Rectangle x:Name="B1" DockPanel.Dock="Bottom" Fill="Transparent" Height="1"/>
<Rectangle x:Name="L1" DockPanel.Dock="Left" Fill="Transparent" Width="1"/>
<Rectangle x:Name="T1" DockPanel.Dock="Top" Fill="Transparent" Height="1"/>
<ContentPresenter x:Name="ContentContainer" HorizontalAlignment="Center" Margin="2,2,2,2" VerticalAlignment="Center"/>
</DockPanel>
<ControlTemplate.Triggers>
<Trigger Property="IsPressed" Value="true">
<Setter Property="Fill" TargetName="R1" Value="{DynamicResource {x:Static SystemColors.ControlLightLightBrushKey}}"/>
<Setter Property="Fill" TargetName="B1" Value="{DynamicResource {x:Static SystemColors.ControlLightLightBrushKey}}"/>
<Setter Property="Fill" TargetName="L1" Value="{DynamicResource {x:Static SystemColors.ControlDarkDarkBrushKey}}"/>
<Setter Property="Fill" TargetName="T1" Value="{DynamicResource {x:Static SystemColors.ControlDarkDarkBrushKey}}"/>
<Setter Property="Margin" TargetName="ContentContainer" Value="3,3,1,1"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
<MenuScrollingVisibilityConverter x:Key="MenuScrollingVisibilityConverter"/>
<Geometry x:Key="DownArrow">M 0,0 L 3.5,4 L 7,0 Z</Geometry>
<Style x:Key="{ComponentResourceKey ResourceId=MenuScrollViewer, TypeInTargetAssembly={x:Type FrameworkElement}}" BasedOn="{x:Null}" TargetType="{x:Type ScrollViewer}">
<Setter Property="HorizontalScrollBarVisibility" Value="Hidden"/>
<Setter Property="VerticalScrollBarVisibility" Value="Auto"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type ScrollViewer}">
<Grid SnapsToDevicePixels="true">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition Height="*"/>
<RowDefinition Height="Auto"/>
</Grid.RowDefinitions>
<Border Grid.Column="0" Grid.Row="1">
<ScrollContentPresenter Margin="{TemplateBinding Padding}"/>
</Border>
<RepeatButton Grid.Column="0" CommandTarget="{Binding RelativeSource={RelativeSource TemplatedParent}}" Command="{x:Static ScrollBar.LineUpCommand}" Focusable="false" Grid.Row="0" Style="{StaticResource MenuScrollButton}">
<RepeatButton.Visibility>
<MultiBinding ConverterParameter="0" Converter="{StaticResource MenuScrollingVisibilityConverter}" FallbackValue="Visibility.Collapsed">
<Binding Path="ComputedVerticalScrollBarVisibility" RelativeSource="{RelativeSource TemplatedParent}"/>
<Binding Path="VerticalOffset" RelativeSource="{RelativeSource TemplatedParent}"/>
<Binding Path="ExtentHeight" RelativeSource="{RelativeSource TemplatedParent}"/>
<Binding Path="ViewportHeight" RelativeSource="{RelativeSource TemplatedParent}"/>
</MultiBinding>
</RepeatButton.Visibility>
<Path Data="{StaticResource UpArrow}" Fill="{DynamicResource {x:Static SystemColors.MenuTextBrushKey}}"/>
</RepeatButton>
<RepeatButton Grid.Column="0" CommandTarget="{Binding RelativeSource={RelativeSource TemplatedParent}}" Command="{x:Static ScrollBar.LineDownCommand}" Focusable="false" Grid.Row="2" Style="{StaticResource MenuScrollButton}">
<RepeatButton.Visibility>
<MultiBinding ConverterParameter="100" Converter="{StaticResource MenuScrollingVisibilityConverter}" FallbackValue="Visibility.Collapsed">
<Binding Path="ComputedVerticalScrollBarVisibility" RelativeSource="{RelativeSource TemplatedParent}"/>
<Binding Path="VerticalOffset" RelativeSource="{RelativeSource TemplatedParent}"/>
<Binding Path="ExtentHeight" RelativeSource="{RelativeSource TemplatedParent}"/>
<Binding Path="ViewportHeight" RelativeSource="{RelativeSource TemplatedParent}"/>
</MultiBinding>
</RepeatButton.Visibility>
<Path Data="{StaticResource DownArrow}" Fill="{DynamicResource {x:Static SystemColors.MenuTextBrushKey}}"/>
</RepeatButton>
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
<ControlTemplate x:Key="{ComponentResourceKey ResourceId=SubmenuContent, TypeInTargetAssembly={x:Type FrameworkElement}}" TargetType="{x:Type ContentControl}">
<Border BorderBrush="#FF959595" BorderThickness="1" Background="#3f3f46">
<Grid>
<ContentPresenter Grid.ColumnSpan="2" Margin="1,0"/>
</Grid>
</Border>
</ControlTemplate>
<ControlTemplate x:Key="{ComponentResourceKey ResourceId=TopLevelHeaderTemplateKey, TypeInTargetAssembly={x:Type MenuItem}}" TargetType="{x:Type MenuItem}">
<Grid SnapsToDevicePixels="true">
<Rectangle x:Name="OuterBorder" RadiusY="2" RadiusX="2"/>
<Rectangle x:Name="Bg" Fill="{TemplateBinding Background}" Margin="1" RadiusY="1" RadiusX="1" Stroke="{TemplateBinding BorderBrush}" StrokeThickness="1"/>
<Rectangle x:Name="InnerBorder" Margin="2"/>
<DockPanel>
<ContentPresenter x:Name="Icon" ContentSource="Icon" Margin="4,0,6,0" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" VerticalAlignment="Center"/>
<Path x:Name="GlyphPanel" Data="{StaticResource Checkmark}" Fill="{TemplateBinding Foreground}" FlowDirection="LeftToRight" Margin="7,0,0,0" Visibility="Collapsed" VerticalAlignment="Center"/>
<ContentPresenter ContentSource="Header" Margin="{TemplateBinding Padding}" RecognizesAccessKey="True" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
</DockPanel>
<Popup x:Name="PART_Popup" AllowsTransparency="true" Focusable="false" HorizontalOffset="1" IsOpen="{Binding IsSubmenuOpen, RelativeSource={RelativeSource TemplatedParent}}" PopupAnimation="{DynamicResource {x:Static SystemParameters.MenuPopupAnimationKey}}" Placement="Bottom" VerticalOffset="-1">
<Themes:SystemDropShadowChrome x:Name="Shdw" Color="Transparent">
<ContentControl x:Name="SubMenuBorder" IsTabStop="false" Template="{DynamicResource {ComponentResourceKey ResourceId=SubmenuContent, TypeInTargetAssembly={x:Type FrameworkElement}}}">
<ScrollViewer CanContentScroll="true" Style="{DynamicResource {ComponentResourceKey ResourceId=MenuScrollViewer, TypeInTargetAssembly={x:Type FrameworkElement}}}">
<ItemsPresenter KeyboardNavigation.DirectionalNavigation="Cycle" Grid.IsSharedSizeScope="true" Margin="2" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" KeyboardNavigation.TabNavigation="Cycle"/>
</ScrollViewer>
</ContentControl>
</Themes:SystemDropShadowChrome>
</Popup>
</Grid>
<ControlTemplate.Triggers>
<Trigger Property="IsSuspendingPopupAnimation" Value="true">
<Setter Property="PopupAnimation" TargetName="PART_Popup" Value="None"/>
</Trigger>
<Trigger Property="Icon" Value="{x:Null}">
<Setter Property="Visibility" TargetName="Icon" Value="Collapsed"/>
</Trigger>
<Trigger Property="IsChecked" Value="true">
<Setter Property="Visibility" TargetName="GlyphPanel" Value="Visible"/>
<Setter Property="Visibility" TargetName="Icon" Value="Collapsed"/>
</Trigger>
<Trigger Property="HasDropShadow" SourceName="PART_Popup" Value="true">
<Setter Property="Margin" TargetName="Shdw" Value="0,0,5,5"/>
<Setter Property="Color" TargetName="Shdw" Value="#71000000"/>
</Trigger>
<Trigger Property="IsHighlighted" Value="true">
<Setter Property="Stroke" TargetName="Bg" Value="#90717070"/>
<Setter Property="Stroke" TargetName="OuterBorder" Value="#50FFFFFF"/>
<Setter Property="Stroke" TargetName="InnerBorder" Value="#50FFFFFF"/>
</Trigger>
<Trigger Property="IsKeyboardFocused" Value="true">
<Setter Property="Stroke" TargetName="Bg" Value="#E0717070"/>
<Setter Property="Fill" TargetName="Bg" Value="{StaticResource MenuItemPressedFill}"/>
<Setter Property="Stroke" TargetName="InnerBorder" Value="#50747272"/>
</Trigger>
<Trigger Property="IsSubmenuOpen" Value="true">
<Setter Property="Stroke" TargetName="Bg" Value="#E0717070"/>
<Setter Property="Fill" TargetName="Bg" Value="{StaticResource MenuItemPressedFill}"/>
<Setter Property="Stroke" TargetName="InnerBorder" Value="#50747272"/>
</Trigger>
<Trigger Property="IsEnabled" Value="false">
<Setter Property="Foreground" Value="#FF9A9A9A"/>
<Setter Property="Fill" TargetName="GlyphPanel" Value="#848589"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
<ControlTemplate x:Key="{ComponentResourceKey ResourceId=TopLevelItemTemplateKey, TypeInTargetAssembly={x:Type MenuItem}}" TargetType="{x:Type MenuItem}">
<Grid SnapsToDevicePixels="true">
<Rectangle x:Name="OuterBorder" RadiusY="2" RadiusX="2"/>
<Rectangle x:Name="Bg" Fill="{TemplateBinding Background}" Margin="1" RadiusY="1" RadiusX="1" Stroke="{TemplateBinding BorderBrush}" StrokeThickness="1"/>
<Rectangle x:Name="InnerBorder" Margin="2"/>
<DockPanel>
<ContentPresenter x:Name="Icon" ContentSource="Icon" Margin="4,0,6,0" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" VerticalAlignment="Center"/>
<Path x:Name="GlyphPanel" Data="{StaticResource Checkmark}" Fill="{TemplateBinding Foreground}" FlowDirection="LeftToRight" Margin="7,0,0,0" Visibility="Collapsed" VerticalAlignment="Center"/>
<ContentPresenter ContentSource="Header" Margin="{TemplateBinding Padding}" RecognizesAccessKey="True" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
</DockPanel>
</Grid>
<ControlTemplate.Triggers>
<Trigger Property="Icon" Value="{x:Null}">
<Setter Property="Visibility" TargetName="Icon" Value="Collapsed"/>
</Trigger>
<Trigger Property="IsChecked" Value="true">
<Setter Property="Visibility" TargetName="GlyphPanel" Value="Visible"/>
<Setter Property="Visibility" TargetName="Icon" Value="Collapsed"/>
</Trigger>
<Trigger Property="IsHighlighted" Value="true">
<Setter Property="Stroke" TargetName="Bg" Value="#90717070"/>
<Setter Property="Stroke" TargetName="OuterBorder" Value="#50FFFFFF"/>
<Setter Property="Stroke" TargetName="InnerBorder" Value="#50FFFFFF"/>
</Trigger>
<Trigger Property="IsKeyboardFocused" Value="true">
<Setter Property="Stroke" TargetName="Bg" Value="#E0717070"/>
<Setter Property="Fill" TargetName="Bg" Value="{StaticResource MenuItemPressedFill}"/>
<Setter Property="Stroke" TargetName="InnerBorder" Value="#50747272"/>
</Trigger>
<Trigger Property="IsEnabled" Value="false">
<Setter Property="Foreground" Value="#FF9A9A9A"/>
<Setter Property="Fill" TargetName="GlyphPanel" Value="#848589"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
<Geometry x:Key="RightArrow">M 0,0 L 4,3.5 L 0,7 Z</Geometry>
<ControlTemplate x:Key="{ComponentResourceKey ResourceId=SubmenuHeaderTemplateKey, TypeInTargetAssembly={x:Type MenuItem}}" TargetType="{x:Type MenuItem}">
<Grid SnapsToDevicePixels="true">
<Rectangle x:Name="Bg" Fill="{TemplateBinding Background}" RadiusY="2" RadiusX="2" Stroke="{TemplateBinding BorderBrush}" StrokeThickness="1"/>
<Rectangle x:Name="InnerBorder" Margin="1" RadiusY="2" RadiusX="2" Stroke="Transparent" StrokeThickness="1"/>
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition MinWidth="24" SharedSizeGroup="MenuItemIconColumnGroup" Width="Auto"/>
<ColumnDefinition Width="4"/>
<ColumnDefinition Width="*"/>
<ColumnDefinition Width="37"/>
<ColumnDefinition SharedSizeGroup="MenuItemIGTColumnGroup" Width="Auto"/>
<ColumnDefinition Width="17"/>
</Grid.ColumnDefinitions>
<ContentPresenter x:Name="Icon" ContentSource="Icon" Margin="1" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" VerticalAlignment="Center"/>
<Border x:Name="GlyphPanel" BorderBrush="#CDD3E6" BorderThickness="1" Background="#E6EFF4" CornerRadius="3" Height="22" Margin="1" Visibility="Hidden" Width="22">
<Path x:Name="Glyph" Data="{StaticResource Checkmark}" Fill="#0C12A1" FlowDirection="LeftToRight" Height="11" Width="9"/>
</Border>
<ContentPresenter Grid.Column="2" ContentSource="Header" Margin="{TemplateBinding Padding}" RecognizesAccessKey="True" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
<TextBlock Grid.Column="4" Margin="{TemplateBinding Padding}" Text="{TemplateBinding InputGestureText}" Visibility="Collapsed"/>
<Path Grid.Column="5" Data="{StaticResource RightArrow}" Fill="{TemplateBinding Foreground}" Margin="4,0,0,0" VerticalAlignment="Center"/>
</Grid>
<Popup x:Name="PART_Popup" AllowsTransparency="true" Focusable="false" HorizontalOffset="-2" IsOpen="{Binding IsSubmenuOpen, RelativeSource={RelativeSource TemplatedParent}}" PopupAnimation="{DynamicResource {x:Static SystemParameters.MenuPopupAnimationKey}}" Placement="Right" VerticalOffset="-3">
<Themes:SystemDropShadowChrome x:Name="Shdw" Color="Transparent">
<ContentControl x:Name="SubMenuBorder" IsTabStop="false" Template="{DynamicResource {ComponentResourceKey ResourceId=SubmenuContent, TypeInTargetAssembly={x:Type FrameworkElement}}}">
<ScrollViewer CanContentScroll="true" Style="{DynamicResource {ComponentResourceKey ResourceId=MenuScrollViewer, TypeInTargetAssembly={x:Type FrameworkElement}}}">
<ItemsPresenter KeyboardNavigation.DirectionalNavigation="Cycle" Grid.IsSharedSizeScope="true" Margin="2" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" KeyboardNavigation.TabNavigation="Cycle"/>
</ScrollViewer>
</ContentControl>
</Themes:SystemDropShadowChrome>
</Popup>
</Grid>
<ControlTemplate.Triggers>
<Trigger Property="IsSuspendingPopupAnimation" Value="true">
<Setter Property="PopupAnimation" TargetName="PART_Popup" Value="None"/>
</Trigger>
<Trigger Property="IsHighlighted" Value="true">
<Setter Property="Stroke" TargetName="InnerBorder" Value="#D1DBF4FF"/>
</Trigger>
<Trigger Property="Icon" Value="{x:Null}">
<Setter Property="Visibility" TargetName="Icon" Value="Collapsed"/>
</Trigger>
<Trigger Property="IsChecked" Value="true">
<Setter Property="Visibility" TargetName="GlyphPanel" Value="Visible"/>
<Setter Property="Visibility" TargetName="Icon" Value="Collapsed"/>
</Trigger>
<Trigger Property="HasDropShadow" SourceName="PART_Popup" Value="true">
<Setter Property="Margin" TargetName="Shdw" Value="0,0,5,5"/>
<Setter Property="Color" TargetName="Shdw" Value="#71000000"/>
</Trigger>
<Trigger Property="IsHighlighted" Value="true">
<Setter Property="Fill" TargetName="Bg" Value="{StaticResource MenuItemSelectionFill}"/>
<Setter Property="Stroke" TargetName="Bg" Value="#8571CBF1"/>
</Trigger>
<Trigger Property="IsEnabled" Value="false">
<Setter Property="Foreground" Value="#FF9A9A9A"/>
<Setter Property="Background" TargetName="GlyphPanel" Value="#EEE9E9"/>
<Setter Property="BorderBrush" TargetName="GlyphPanel" Value="#DBD6D6"/>
<Setter Property="Fill" TargetName="Glyph" Value="#848589"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
<Style x:Key="MenuItemStyle1" TargetType="{x:Type MenuItem}">
<Setter Property="HorizontalContentAlignment" Value="{Binding HorizontalContentAlignment, RelativeSource={RelativeSource AncestorType={x:Type ItemsControl}}}"/>
<Setter Property="VerticalContentAlignment" Value="{Binding VerticalContentAlignment, RelativeSource={RelativeSource AncestorType={x:Type ItemsControl}}}"/>
<Setter Property="Background" Value="Transparent"/>
<Setter Property="Template" Value="{DynamicResource {ComponentResourceKey ResourceId=SubmenuItemTemplateKey, TypeInTargetAssembly={x:Type MenuItem}}}"/>
<Style.Triggers>
<Trigger Property="Role" Value="TopLevelHeader">
<Setter Property="Padding" Value="7,2,8,3"/>
<Setter Property="Template" Value="{DynamicResource {ComponentResourceKey ResourceId=TopLevelHeaderTemplateKey, TypeInTargetAssembly={x:Type MenuItem}}}"/>
</Trigger>
<Trigger Property="Role" Value="TopLevelItem">
<Setter Property="Padding" Value="7,2,8,3"/>
<Setter Property="Template" Value="{DynamicResource {ComponentResourceKey ResourceId=TopLevelItemTemplateKey, TypeInTargetAssembly={x:Type MenuItem}}}"/>
</Trigger>
<Trigger Property="Role" Value="SubmenuHeader">
<Setter Property="Padding" Value="2,3,2,3"/>
<Setter Property="Template" Value="{DynamicResource {ComponentResourceKey ResourceId=SubmenuHeaderTemplateKey, TypeInTargetAssembly={x:Type MenuItem}}}"/>
</Trigger>
<Trigger Property="Role" Value="SubmenuItem">
<Setter Property="Padding" Value="2,3,2,3"/>
</Trigger>
</Style.Triggers>
</Style>
让您的 Menu 仍然使用您的 MainMenu 样式，但让每个子 MenuItem 使用 Blend 生成的样式。例如，尝试
<MenuItem Header="_File" Style="{DynamicResource MenuItemStyle1}">
看起来像这样：
不确定这与您正在寻找的内容有多接近，但希望能让您走上正确的道路。