樣式程式碼:

 <Style x:Key="ExpanderToggleButtonStyle" TargetType="{x:Type ToggleButton}">
        <Setter Property="FocusVisualStyle" Value="{x:Null}"/>
        
        <Setter Property="Height" Value="35" />
        <Setter Property="Background" Value="SlateGray" />
        <
 
Setter Property="Foreground" Value="Gainsboro"/>
        <Setter Property="FontSize" Value="20" />
        <Setter Property="FontFamily" Value="宋體" />
        <Setter Property="FontWeight" Value="Bold" />
        <Setter Property="BorderThickness" Value="0"/>
        <Setter Property
 
="HorizontalContentAlignment" Value="Center"/>
        <Setter Property="VerticalContentAlignment" Value="Center"/>
        <Setter Property="Width" Value="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=Expander}, Path=ActualWidth}"></Setter>
        <Setter 
 
Property="Padding" Value="10 5"/>
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type ToggleButton}">
                    <Canvas Width="{TemplateBinding Width}" Height="{TemplateBinding Height}" 
                    Background="{TemplateBinding Background}" SnapsToDevicePixels="True">
                        <Canvas x:Name="canvNormal" Visibility="Visible" 
                     Width="{TemplateBinding Width}" Height="{TemplateBinding Height}" 
                     Background="{TemplateBinding Background}" SnapsToDevicePixels="True" Canvas.Right="0">
                            <Path Data="M 0 0 L 6 6  12 0 " Stroke="LightSteelBlue" StrokeThickness="2" Canvas.Right="5" Canvas.Top="10"/>
                            <Path Data="M 0 0 L 6 6  12 0 " Stroke="LightSteelBlue" StrokeThickness="2" Canvas.Right="5" Canvas.Top="15"/>
                        </Canvas>
                        <Canvas x:Name="canvChecked" Visibility="Hidden" 
                     Width="{TemplateBinding Width}" Height="{TemplateBinding Height}" 
                     Background="{TemplateBinding Background}" SnapsToDevicePixels="True" Canvas.Right="0">
                            <Path Data="M 0 0 L 6 -6  12 0 " Stroke="LightSteelBlue" StrokeThickness="2" Canvas.Right="5" Canvas.Top="15"/>
                            <Path Data="M 0 0 L 6 -6  12 0 " Stroke="LightSteelBlue" StrokeThickness="2" Canvas.Right="5" Canvas.Top="20"/>
                        </Canvas>

                        <ContentPresenter 
                            HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" 
                     Margin="{TemplateBinding Padding}" 
                     RecognizesAccessKey="True"                       
                     SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" 
                     VerticalAlignment="{TemplateBinding VerticalContentAlignment}"/>
                    </Canvas>

                    <ControlTemplate.Triggers>
                        <Trigger Property="IsPressed" Value="true">
                            <Setter Property="Background" Value="SlateGray" />
                        </Trigger>
                        <Trigger Property="IsChecked" Value="true">
                            <Setter Property="Visibility" TargetName="canvChecked" Value="Visible" />
                            <Setter Property="Visibility" TargetName="canvNormal" Value="Hidden" />
                        </Trigger>
                        <Trigger Property="IsEnabled" Value="false">
                            <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}"/>
                        </Trigger>
                    </ControlTemplate.Triggers>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>
    <Style x:Key="ExpanderStyle" TargetType="{x:Type Expander}">
        <Setter Property="Foreground" Value="#FF217cb5"/>
        <Setter Property="FontFamily" Value="宋體" />
        <Setter Property="FontSize" Value="14" />
        <Setter Property="Background" Value="Transparent"/>
        <Setter Property="HorizontalContentAlignment" Value="Stretch"/>
        <Setter Property="VerticalContentAlignment" Value="Stretch"/>
        <Setter Property="BorderBrush" Value="Transparent"/>
        <Setter Property="BorderThickness" Value="1"/>
        <Setter Property="HorizontalAlignment" Value="Center"/>
        
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type Expander}">
                    <Border BorderBrush="{TemplateBinding BorderBrush}" 
                            BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" CornerRadius="0" SnapsToDevicePixels="True"
                            Width="{TemplateBinding Width}">
                        <Grid>
                            <Grid.RowDefinitions>
                                <RowDefinition Height="auto"/>
                                <RowDefinition Height="auto"/>
                            </Grid.RowDefinitions>
                        
                        
                            <ToggleButton x:Name="HeaderSite"  Grid.Row="0"
                          ContentTemplate="{TemplateBinding HeaderTemplate}" 
                          ContentTemplateSelector="{TemplateBinding HeaderTemplateSelector}"
                          Content="{TemplateBinding Header}"                                   
                          IsChecked="{Binding IsExpanded, Mode=TwoWay, RelativeSource={RelativeSource TemplatedParent}}"                                  
                          Style="{DynamicResource ExpanderToggleButtonStyle}" />
                            <ContentPresenter x:Name="ExpandSite" Grid.Row="1"
                                              ContentTemplate="{TemplateBinding ContentTemplate}" Content="{TemplateBinding Content}" ContentStringFormat="{TemplateBinding ContentStringFormat}" Focusable="False" 
                                              HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" Margin="{TemplateBinding Padding}" Visibility="Collapsed" VerticalAlignment="{TemplateBinding VerticalContentAlignment}"/>
                        </Grid>
                    </Border>
                    <ControlTemplate.Triggers>
                        <Trigger Property="IsExpanded" Value="True">
                            <Setter Property="Visibility" TargetName="ExpandSite" Value="Visible"/>
                        </Trigger>
                        <Trigger Property="IsEnabled" Value="False">
                            <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}"/>
                        </Trigger>
                    </ControlTemplate.Triggers>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>

效果圖: