private double GetRelativeOffset()
{
ScrollContentPresenter scp = MainScrollViewer.GetFirstDescendantOfType <ScrollContentPresenter>();
FrameworkElement content = scp?.Content as FrameworkElement;
GeneralTransform transform = ScrollingTabs.TransformToVisual(content);
return(transform.TransformPoint(new Point(0, 0)).Y - MainScrollViewer.VerticalOffset);
}