ShrlAlgoToolkit/WPFluent/Controls/Separator/Separator.xaml

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

    <Style TargetType="{x:Type Separator}">
        <Setter Property="BorderBrush" Value="{DynamicResource DividerStrokeColorDefaultBrush}" />
        <Setter Property="Background" Value="Transparent" />
        <Setter Property="Margin" Value="0" />
        <Setter Property="BorderThickness" Value="1,1,0,0" />
        <Setter Property="Focusable" Value="False" />
        <Setter Property="SnapsToDevicePixels" Value="True" />
        <Setter Property="OverridesDefaultStyle" Value="True" />
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type Separator}">
                    <Border
                        Background="{TemplateBinding Background}"
                        BorderBrush="{TemplateBinding BorderBrush}"
                        BorderThickness="{TemplateBinding BorderThickness}"
                        Margin="{TemplateBinding Margin}"
                        Width="{TemplateBinding Width}" />
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>

</ResourceDictionary>