Here’s my Slider:

<Style x:Key="CustomThumbStyle"
       TargetType="Thumb">
    <Setter Property="Width"
            Value="10" />
    <Setter Property="Height"
            Value="20" />
    <Setter Property="Padding"
            Value="5" />
    <Setter Property="Background"
            Value="Red" />
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="Thumb">
                <Grid>
                    <Rectangle Width="{TemplateBinding Width}"
                               Height="{TemplateBinding Height}"
                               Fill="Green" />
                    <Ellipse Width="10"
                             Height="10"
                             Fill="Red"
                             HorizontalAlignment="Center"
                             VerticalAlignment="Center" />
                </Grid>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

<Slider x:Name="videoPlayerSlider"
        Minimum="0"
        Maximum="100"
        HorizontalAlignment="Stretch"
        VerticalAlignment="Bottom"
        Thumb.DragStarted="OnSliderDragStarted_Click"
        Thumb.DragDelta="OnSliderDragDelta_Drag"
        Thumb.DragCompleted="OnSliderDragCompleted_Click"
        Value="0"
        Height="20"
        Margin="0,0,0,-20">
    <Slider.Template>
        <ControlTemplate TargetType="Slider">
            <Grid>
                <Track x:Name="PART_Track">
                    <Track.DecreaseRepeatButton>
                        <RepeatButton Command="{x:Static Slider.DecreaseLarge}"
                                      Background="Orange"
                                      BorderThickness="0"
                                      CommandTarget="{Binding RelativeSource={RelativeSource TemplatedParent}}"
                                      Focusable="false" />
                    </Track.DecreaseRepeatButton>
                    <Track.Thumb>
                        <Thumb Style="{StaticResource CustomThumbStyle}" />
                    </Track.Thumb>
                    <Track.IncreaseRepeatButton>
                        <RepeatButton Command="{x:Static Slider.IncreaseLarge}"
                                      Background="Orange"
                                      BorderThickness="0"
                                      CommandTarget="{Binding RelativeSource={RelativeSource TemplatedParent}}"
                                      Focusable="false" />
                    </Track.IncreaseRepeatButton>
                </Track>
            </Grid>
        </ControlTemplate>
    </Slider.Template>
</Slider>

Which renders as:

How can I remove that rounded borders?