How to hidden BorderBrush White use Popup MaterialDesign Wpf

I am facing problem while using popupbox in materialDesign . That is it appears 2 white borders as shown, and want to turn it off. I have read and tried to use AllowsTranspency but it does not. Can someone help me on this issue?

 <materialDesign:PopupBox StaysOpen="False" PlacementMode="BottomAndAlignCentres">
                                    <materialDesign:PopupBox.ToggleContent>
                                        <TextBlock Text="Change" Margin="0 0 0 0" Foreground="WhiteSmoke"/>
                                    </materialDesign:PopupBox.ToggleContent>
                                    <StackPanel>
                                        <Grid>
                                            <ScrollViewer Grid.Row="0" Background="#212121" HorizontalScrollBarVisibility="Hidden" VerticalScrollBarVisibility="Hidden" BorderBrush="Transparent">
                                                <ListBox Name="lstbox" SelectionMode="Extended" ItemsSource="{Binding lstNetworkInterfaces}" Grid.Row="1" Margin="5" Background="#212121" >
                                                    <ListBox.Template>
                                                        <ControlTemplate TargetType="ItemsControl">
                                                            <Border>
                                                                <ItemsPresenter />
                                                            </Border>
                                                        </ControlTemplate>
                                                    </ListBox.Template>
                                                    <ListBox.ItemsPanel>
                                                        <ItemsPanelTemplate>
                                                            <StackPanel />
                                                        </ItemsPanelTemplate>
                                                    </ListBox.ItemsPanel>
                                                    <ListBox.ItemTemplate>
                                                        <DataTemplate>
                                                            <Border Name="HightlightBorder" Grid.Column="0" Grid.ColumnSpan="2"  BorderThickness="0 0 0 1" BorderBrush="Gray" Margin="5 5 10 5" Background="{Binding BackgroundChoose}">
                                                                <!--<Button Background="Transparent" BorderBrush="Transparent" >-->
                                                                <i:Interaction.Triggers>
                                                                    <i:EventTrigger EventName="MouseLeftButtonUp">
                                                                        <i:InvokeCommandAction Command="{Binding Path=DataContext.SelectItemsCommand, RelativeSource= {RelativeSource FindAncestor,
                                                                        AncestorType={x:Type ItemsControl}}}" CommandParameter="{Binding}"></i:InvokeCommandAction>
                                                                    </i:EventTrigger>
                                                                </i:Interaction.Triggers>
                                                                <StackPanel Margin="25 0 70 0">
                                                                    <TextBlock Margin="0 10 0 0" Text="{Binding NetworkCardName}" HorizontalAlignment="Center" Foreground="White" FontSize="17" FontWeight="DemiBold"/>
                                                                    <DockPanel Margin="3 15 0 5">
                                                                        <TextBlock Text="Description . . . . . . . . . . . . . . . . . . :   " Foreground="WhiteSmoke"/>
                                                                        <TextBlock Text="{Binding Description}" Foreground="WhiteSmoke" FontWeight="DemiBold"/>
                                                                    </DockPanel>
                                                                    <DockPanel Margin="0 15 0 5">
                                                                        <TextBlock Text=" Physical Address/MAC . . . . . . . . :   " Foreground="WhiteSmoke"/>
                                                                        <TextBlock Text="{Binding MAC}" Foreground="WhiteSmoke" FontWeight="DemiBold"/>
                                                                    </DockPanel>
                                                                    <DockPanel Margin="3 15 0 5">
                                                                        <TextBlock Text="Status. . . . . . . . . . . . . . . . . . . . . . . .:   " Foreground="WhiteSmoke"/>
                                                                        <TextBlock Text="{Binding IpAdress}" Foreground="WhiteSmoke" FontWeight="DemiBold" Margin="0 0 0 15"/>
                                                                    </DockPanel>
                                                                </StackPanel>
                                                                <!--</Button>-->
                                                            </Border>
                                                        </DataTemplate>
                                                    </ListBox.ItemTemplate>
                                                </ListBox>
                                            </ScrollViewer>
                                        </Grid>
                                    </StackPanel>
                                </materialDesign:PopupBox>