public class FixedMasterDetailPageRenderer: MasterDetailPageRenderer
    {
        protected override void OnElementChanged(VisualElement oldElement, VisualElement newElement)
        {
            base.OnElementChanged(oldElement, newElement);

            var detailContainer = GetChildAt(0);
            var masterContainer = GetChildAt(1);

            // Use reflection to modify MasterDetailContainer's (internal class) TopPadding
            var topPadding = detailContainer.GetType().GetProperty("TopPadding");
            topPadding.SetValue(detailContainer, 0);
            topPadding.SetValue(masterContainer, 0);
        }
    }