Shaker/Avalonia/SukiUI/Theme/Separator.axaml

<ResourceDictionary xmlns="https://github.com/avaloniaui"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
    <ControlTheme x:Key="SukiSeparatorStyle" TargetType="Separator">
        <Setter Property="Background" Value="Transparent" />
        <Setter Property="BorderBrush" Value="Transparent" />
        <Setter Property="BorderThickness" Value="0" />
        <Setter Property="CornerRadius" Value="0" />
        <Setter Property="Foreground" Value="{DynamicResource SukiLightBorderBrush}" />
        <Setter Property="MinHeight" Value="1" />
        <Setter Property="Height" Value="1" />
        <Setter Property="Margin" Value="0" />
        <Setter Property="Template">
            <ControlTemplate>
                <Border Name="PART_RootBorder"
                        Background="{TemplateBinding Background}"
                        BorderBrush="{TemplateBinding BorderThickness}"
                        BorderThickness="{TemplateBinding BorderThickness}"
                        CornerRadius="{TemplateBinding CornerRadius}">
                    <Rectangle Name="PART_Content" Fill="{TemplateBinding Foreground}" />
                </Border>
            </ControlTemplate>
        </Setter>

        <Style Selector="^ /template/ Border#PART_RootBorder">
            <Setter Property="ClipToBounds" Value="True" />
        </Style>

        <Style Selector="^ /template/ Rectangle#PART_Content">
            <Setter Property="Height" Value="1" />
            <Setter Property="HorizontalAlignment" Value="Stretch" />
            <Setter Property="VerticalAlignment" Value="Center" />
        </Style>
    </ControlTheme>
    <ControlTheme x:Key="{x:Type Separator}" TargetType="Separator"
                  BasedOn="{StaticResource SukiSeparatorStyle}" />
</ResourceDictionary>