Virgo_ST/VirgoUI/Styles/Expander.xaml

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">

    <Style x:Key="ExpanderHeaderFocusVisual">
        <Setter Property="Control.Template">
            <Setter.Value>
                <ControlTemplate>
                    <Border>
                        <Rectangle Margin="0" SnapsToDevicePixels="true" Stroke="Black" StrokeThickness="1" StrokeDashArray="1 2"/>
                    </Border>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>

    <SolidColorBrush x:Key="Expander_Header_BG" Color="#FF6A82AD"/>
    <SolidColorBrush x:Key="Expander_Header_BD" Color="Black"/>
    <SolidColorBrush x:Key="Expander_Header_BG_HighLight" Color="#FFD6E4FF"/>

    <Style x:Key="ExpanderDownHeaderStyle" TargetType="{x:Type ToggleButton}">
        <Setter Property="FontSize" Value="14"/>
        <Setter Property="FontFamily" Value="Arial"/>
        <Setter Property="Foreground" Value="{DynamicResource FG_Black}"/>
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type ToggleButton}">
                    <Grid Cursor="Hand" Background="Transparent">
                        <Grid SnapsToDevicePixels="False" Margin="0,5">
                            <Grid.ColumnDefinitions>
                                <ColumnDefinition Width="17"/>
                                <ColumnDefinition />
                            </Grid.ColumnDefinitions>
                            <Border x:Name="OuterBorder" Grid.Column="0" HorizontalAlignment="Right" Height="15" BorderBrush="{DynamicResource Expander_Header_BD}" BorderThickness="1" Background="{DynamicResource Expander_Header_BG}" CornerRadius="2" VerticalAlignment="Center" Width="15">
                                <Grid>
                                    <Rectangle x:Name="Path1" Fill="White" Height="2" Width="9"/>
                                    <Rectangle x:Name="Path2" Fill="White" Height="9" Width="2"/>
                                </Grid>
                            </Border>
                            <ContentPresenter Grid.Column="1" HorizontalAlignment="Left" Margin="5,0,0,0" RecognizesAccessKey="True" SnapsToDevicePixels="True" VerticalAlignment="Center"/>
                        </Grid>
                    </Grid>
                    <ControlTemplate.Triggers>
                        <Trigger Property="IsChecked" Value="true">
                            <Setter Property="Visibility" TargetName="Path2" Value="Collapsed"/>
                            <Setter Property="Background" TargetName="OuterBorder" Value="{DynamicResource Expander_Header_BG_HighLight}"/>
                            <Setter Property="Fill" TargetName="Path1" Value="Black"/>
                        </Trigger>
                        <Trigger Property="IsMouseOver" Value="true"/>
                        <Trigger Property="IsPressed" Value="true">
                            <Setter Property="Background" TargetName="OuterBorder" Value="{DynamicResource Expander_Header_BG_HighLight}"/>
                        </Trigger>
                    </ControlTemplate.Triggers>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>

    <Style x:Key="ExpanderRightHeaderStyle" TargetType="{x:Type ToggleButton}">
        <Setter Property="FontSize" Value="14"/>
        <Setter Property="FontFamily" Value="Arial"/>
        <Setter Property="Foreground" Value="{DynamicResource FG_Black}"/>
        <Setter Property="Background" Value="{DynamicResource Expander_Header_BG}"/>
        <Setter Property="BorderBrush" Value="{DynamicResource Expander_Header_BD}"/>
        <Setter Property="Border.CornerRadius" Value="2"/>
        <Setter Property="Opacity" Value="1"/>
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type ToggleButton}">
                    <Grid Cursor="Hand" Background="Transparent">
                        <Grid.LayoutTransform>
                            <TransformGroup>
                                <TransformGroup.Children>
                                    <TransformCollection>
                                        <RotateTransform Angle="-90"/>
                                    </TransformCollection>
                                </TransformGroup.Children>
                            </TransformGroup>
                        </Grid.LayoutTransform>
                        <Grid SnapsToDevicePixels="False" Margin="0,5">
                            <Grid.ColumnDefinitions>
                                <ColumnDefinition Width="17"/>
                                <ColumnDefinition />
                            </Grid.ColumnDefinitions>
                            <Border x:Name="OuterBorder" Grid.Column="0" HorizontalAlignment="Right" Height="15" BorderBrush="{DynamicResource Expander_Header_BD}" BorderThickness="1" Background="{DynamicResource Expander_Header_BG}" CornerRadius="2" VerticalAlignment="Center" Width="15">
                                <Grid>
                                    <Rectangle x:Name="Path1" Fill="White" Height="2" Width="9">
                                        <Rectangle.LayoutTransform>
                                            <TransformGroup>
                                                <TransformGroup.Children>
                                                    <TransformCollection>
                                                        <RotateTransform Angle="-90"/>
                                                    </TransformCollection>
                                                </TransformGroup.Children>
                                            </TransformGroup>
                                        </Rectangle.LayoutTransform>
                                    </Rectangle>
                                    <Rectangle x:Name="Path2" Fill="White" Height="9" Width="2">
                                        <Rectangle.LayoutTransform>
                                            <TransformGroup>
                                                <TransformGroup.Children>
                                                    <TransformCollection>
                                                        <RotateTransform Angle="-90"/>
                                                    </TransformCollection>
                                                </TransformGroup.Children>
                                            </TransformGroup>
                                        </Rectangle.LayoutTransform>
                                    </Rectangle>
                                </Grid>
                            </Border>
                            <ContentPresenter Grid.Column="1" HorizontalAlignment="Center" VerticalAlignment="Center" Margin="5,0" RecognizesAccessKey="True" SnapsToDevicePixels="True"/>
                        </Grid>
                    </Grid>
                    <ControlTemplate.Triggers>
                        <Trigger Property="IsChecked" Value="true">
                            <Setter Property="Visibility" TargetName="Path2" Value="Collapsed"/>
                            <Setter Property="Background" TargetName="OuterBorder" Value="{DynamicResource Expander_Header_BG_HighLight}"/>
                            <Setter Property="Fill" TargetName="Path1" Value="Black"/>
                        </Trigger>
                        <Trigger Property="IsMouseOver" Value="true"/>
                        <Trigger Property="IsPressed" Value="true">
                            <Setter Property="Background" TargetName="OuterBorder" Value="{DynamicResource Expander_Header_BG_HighLight}"/>
                        </Trigger>
                    </ControlTemplate.Triggers>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>

    <Style TargetType="{x:Type Expander}">
        <Setter Property="BorderThickness" Value="0"/>
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type Expander}">
                    <Grid>
                        <DockPanel>
                            <ToggleButton x:Name="HeaderSite" 
										  ContentTemplate="{TemplateBinding HeaderTemplate}" 
										  ContentTemplateSelector="{TemplateBinding HeaderTemplateSelector}" 
										  Content="{TemplateBinding Header}" 
										  DockPanel.Dock="Top" 
										  FocusVisualStyle="{StaticResource ExpanderHeaderFocusVisual}"
										  HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}" 
										  IsChecked="{Binding IsExpanded, Mode=TwoWay, RelativeSource={RelativeSource TemplatedParent}}" 
										  MinWidth="0" 
										  MinHeight="0" 
										  Style="{StaticResource ExpanderDownHeaderStyle}" 
										  VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}"/>
                            <ContentPresenter x:Name="ExpandSite" Focusable="false" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" Visibility="Collapsed" VerticalAlignment="{TemplateBinding VerticalContentAlignment}" DockPanel.Dock="Bottom"/>
                        </DockPanel>
                    </Grid>
                    <ControlTemplate.Triggers>
                        <Trigger Property="IsExpanded" Value="true">
                            <Setter Property="Visibility" TargetName="ExpandSite" Value="Visible"/>
                        </Trigger>
                        <Trigger Property="ExpandDirection" Value="Right">
                            <Setter Property="DockPanel.Dock" TargetName="ExpandSite" Value="Right"/>
                            <Setter Property="DockPanel.Dock" TargetName="HeaderSite" Value="Left"/>
                            <Setter Property="Style" TargetName="HeaderSite" Value="{StaticResource ExpanderRightHeaderStyle}"/>
                        </Trigger>
                        <Trigger Property="IsEnabled" Value="false">
                            <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}"/>
                        </Trigger>
                    </ControlTemplate.Triggers>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>

</ResourceDictionary>