How to remove maring between ListView.GroupHeaderTemplate and first item in list?

Hi, I'm trying to style ListView.GroupHeaderTemplate, so it has backgroundColor.

On iOS it looks great.
On UWP, given XAML below, I receive unwanted space between GroupHeader and first item in group. How can I remove it? I've tried setting margins, spacing and padding of probably every item in GroupHeaderTemplate but with no avail.

Here is link to repo with faulty code - https://bitbucket.org/Leroom/xamarinlistgroupheadermargin/overview
Link to XAML - https://bitbucket.org/Leroom/xamarinlistgroupheadermargin/src/f2881114a65c57dde92b2f926bd088d16f9c06a8/ListGroupHeaderMarginIssue/ListGroupHeaderMarginIssue/MainPage.xaml?at=master&fileviewer=file-view-default

And the XAML itself

`<?xml version="1.0" encoding="utf-8" ?>

<ListView.GroupHeaderTemplate>







</ListView.GroupHeaderTemplate>
<ListView.Header></ListView.Header>
<ListView.ItemTemplate>



<Grid.RowDefinitions>



</Grid.RowDefinitions>

        <Label Grid.Row="0"
               Grid.Column="0"
               Text="{Binding LineOne}"
               LineBreakMode="TailTruncation"
               FontSize="16"
               TextColor="#4d4d4d"
               VerticalOptions="CenterAndExpand" />

        <Label Grid.Row="1"
               Grid.Column="0"
               Text="{Binding LineTwo}"
               FontSize="14"
               TextColor="#808080"/>

        <Label Grid.Row="2"
               Grid.Column="0"
               Text="{Binding LineThree}"
               FontSize="14"
               TextColor="#808080"/>
      </Grid>
    </ViewCell>
  </DataTemplate>
</ListView.ItemTemplate>
<ListView.Footer></ListView.Footer>

`

and classes used to create viewModel

`using System.Collections.ObjectModel;

namespace ListGroupHeaderMarginIssue
{
public class ViewModel
{
public ViewModel()
{
ItemGroups = new ObservableCollection();
}

    public ObservableCollection<ViewModelItemGroup> ItemGroups { get; set; }
}

public class ViewModelItemGroup : ObservableCollection<ViewModelItem>
{
    public string  DisplayName { get; set; }
}

public class ViewModelItem
{
    public ViewModelItem()
    {
    }

    public ViewModelItem(string lineOne, string lineTwo, string lineThree)
    {
        LineOne = lineOne;
        LineTwo = lineTwo;
        LineThree = lineThree;
    }

    public string LineOne { get; set; }
    public string LineTwo { get; set; }
    public string LineThree { get; set; }
}

}
`