Hello,

This line is part of the Event Title - its style is set through EventTitle's LineStyle property.

Here is a link to the style guide for the Event Titles.

Here is a sample line style:

<Style x:Key="EventTitleStyle" TargetType="ig:EventTitle">
    <Setter Property="LineStyle">
        <Setter.Value>
            <Style TargetType="Line">
                <Setter Property="StrokeThickness" Value="1" />
                <Setter Property="Stroke" Value="Black" />
                <Setter Property="Canvas.ZIndex" Value="-1" />
            </Style>
        </Setter.Value>
    </Setter>
</Style>

Here is how to apply the line style:

<ig:XamTimeline EventTitleBottomStyle="{StaticResource EventTitleStyle}"
                EventTitleTopStyle="{StaticResource EventTitleStyle}">

Thanks,

Nikolay