xamarin forms - ios - listview header - showing bold border? - xaml

Question

Please see below image
please see below code
//PopUp.Xaml
<ListView.Header>
<Frame>
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="*"/>
<RowDefinition Height="Auto"/>
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="30*" />
<ColumnDefinition Width="25*" />
<ColumnDefinition Width="25*" />
<ColumnDefinition Width="20*" />
</Grid.ColumnDefinitions>
<Label Grid.Column="0" Grid.Row="0" Text="Product"
HorizontalOptions="Center"/>
<Label Grid.Column="1" Grid.Row="0"
Text="Quantity"
HorizontalOptions="Center"/>
<Label Grid.Column="2" Grid.Row="0"
Text="Price"
HorizontalOptions="Center"/>
<Label Grid.Column="3" Grid.Row="0"
Text="Sub"
HorizontalOptions="Center"/>
<BoxView Grid.Row="1"
Grid.ColumnSpan="4"
HeightRequest="1"
BackgroundColor="LightGray"/>
</Grid>
</Frame>
</ListView.Header>
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<Grid Padding="10" RowSpacing="10" ColumnSpacing="10">
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition Height="*"/>
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="43*" />
<ColumnDefinition Width="8*" />
<ColumnDefinition Width="25*" />
<ColumnDefinition Width="24*" />
</Grid.ColumnDefinitions>
<Label Grid.Column="0" Text="{Binding OrderModel_Id}" VerticalOptions="End"/>
<Label Grid.Column="1" Grid.Row="0" Text="{Binding User_Name}" VerticalOptions="End"/>
<Label Grid.Column="0" Grid.Row="0" HorizontalOptions="StartAndExpand" VerticalOptions="StartAndExpand" Text="{Binding Product_Id, Converter={StaticResource converter}}"/>
<Label Grid.Column="1" Grid.Row="0" HorizontalOptions="CenterAndExpand" VerticalOptions="CenterAndExpand" Text="{Binding Quantity}"/>
<Label Grid.Column="2" Grid.Row="0" HorizontalOptions="CenterAndExpand" VerticalOptions="CenterAndExpand" Text="{Binding PriceOf_Item, StringFormat='£{0:0.00}'}"/>
<Label Grid.Column="3" Grid.Row="0" HorizontalOptions="CenterAndExpand" VerticalOptions="CenterAndExpand" Text="{Binding SubtotalForThis_Item, StringFormat='£{0:0.00}'}"/>
</Grid>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
</StackLayout>
</pages:PopupPage>
My Q being why does the popUp header of the listview...appear with a bold border below it? only on ios...not on android...I would like to remove it please. does anyone know how?