title: Align header and items in grouped GridView
body: <p>I'm working on an UWP app and got trouble aligning headers with items in a grouped GridView, here's a picture of what I mean by that:</p>
  
  <p><a href="https://i.stack.imgur.com/6rnqv.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/6rnqv.png" alt="Header title not aligned with item"></a></p>
  
  <p>This is a simple GridView with no fancy styles applied or whatever and I thought this should work out of the box, but it doesn't.</p>
  
  <p>Using the live visual tree from VS 2015 I found out that this is a 12px left margin on a ContentPresenter and a Rectangle inside the GridView header:</p>
  
  <p><a href="https://i.stack.imgur.com/JeGio.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/JeGio.png" alt="StackPanel and Rectangle have 12px left margin"></a></p>
  
  <p>The StackPanel is inside the header and it houses the grid from my header template (see below for XAML) wrapped in a ContentPresenter (which has that 12px margin) and a Rectangle (which also has that margin) below that; this appears to be the ruler below the group title.</p>
  
  <p>However, I haven't got the foggiest idea how to change that margin. I tried setting the header template in the GridView's GroupStyle</p>
  
  <pre><code> &lt;GridView Grid.Row="1"
          ItemsSource="{Binding Source={StaticResource exercisesCollection}}"
          ItemTemplate="{StaticResource gridViewTemplate}"
          SelectionMode="None"
          CanDragItems="True"&gt;
      &lt;GridView.GroupStyle&gt;
         &lt;GroupStyle HidesIfEmpty="True"&gt;
            &lt;GroupStyle.HeaderTemplate&gt;
               &lt;DataTemplate&gt;
                  &lt;Grid&gt;
                     &lt;TextBlock Text="{Binding Path=Name}" /&gt;
                  &lt;/Grid&gt;
               &lt;/DataTemplate&gt;
            &lt;/GroupStyle.HeaderTemplate&gt;
         &lt;/GroupStyle&gt;
      &lt;/GridView.GroupStyle&gt;
   &lt;/GridView&gt;
  </code></pre>
  
  <p>but to no avail. Is there any way to fix this behavior?</p>