Получение свойства Margin из элементов ItemsControl

<Grid>
    <Rectangle Height="7" Fill="#FF00A8FF" Margin="10,0,1830,0">
 
    </Rectangle>
    <ItemsControl x:Name="Steps" ItemsSource="{Binding StepsItems}">
        <ItemsControl.ItemsPanel>
            <ItemsPanelTemplate>
                <StackPanel Orientation="Horizontal" VerticalAlignment="Center" />
            </ItemsPanelTemplate>
        </ItemsControl.ItemsPanel>
 
        <ItemsControl.ItemTemplate>
 
            <DataTemplate>
 
                <DataTemplate.Resources>
                    <Style TargetType="{x:Type Ellipse}">
                        <Setter Property="Margin" Value="10,15,0,0"/>
                    </Style>
                    <Style TargetType="{x:Type TextBlock}">
                        <Setter Property="Margin" Value="10,0,0,0"/>
                        <Setter Property="TextTrimming" Value="CharacterEllipsis"/>
                    </Style>
                </DataTemplate.Resources>
 
                <StackPanel MaxWidth="75">
                    <Grid>
                        <Ellipse x:Name="EllipseOuter"  Width="20" Height="20" Fill="{Binding OuterColor}" />
                        <Ellipse x:Name="EllipseInner"  Width="10" Height="10" Fill="{Binding InnerColor}" />
                    </Grid>
 
                    <TextBlock Text="{Binding Name}" HorizontalAlignment="Center" />
                </StackPanel>
 
                <DataTemplate.Triggers>
                    <DataTrigger Binding="{Binding IsCompleted}" Value="true">
                        <Setter TargetName="EllipseInner" Property="Fill" Value="{Binding CompletedColor}" />
                    </DataTrigger>
                    <DataTrigger Binding="{Binding IsCompleted}" Value="false">
                        <Setter TargetName="EllipseInner" Property="Fill" Value="{Binding InnerColor}" />
                    </DataTrigger>
                </DataTemplate.Triggers>
 
 
            </DataTemplate>
        </ItemsControl.ItemTemplate>
    </ItemsControl>
</Grid>

<Grid>
    <Canvas x:Name="PageTransitor" />
    <local:PageTransition/>
    <local:StepProgressBar x:Name="FirmwareBar" Margin="0,0,0,0">
        <local:StepProgressBar.StepsItems>
          <local:Step Name="1" OuterColor="#FF100E87"/>
          <local:Step Name="2" OuterColor="#FF0089FF" IsCompleted="False" CompletedColor="#FF0089FF"/>
          <local:Step Name="3" OuterColor="#FF0089FF" IsCompleted="False" CompletedColor="#FF0089FF"/>
          <local:Step Name="4" OuterColor="#FF0089FF" IsCompleted="False" CompletedColor="#FF0089FF"/>
        </local:StepProgressBar.StepsItems>
 
    </local:StepProgressBar>
    
</Grid>

<Grid HorizontalAlignment="Left">
    <Rectangle Height="7" Fill="#FF00A8FF" Margin="20 0"  VerticalAlignment="Center"/>
 
    <ItemsControl x:Name="Steps" ItemsSource="{Binding StepsItems}">