private void OnAddedToVisualTree()
{
focusSubscription = Application.FocusManager.SubscribeUnmanaged(nameof(FocusManager.FocusedControl), FocusChanged);
SynchronizeForLifetime(nameof(HorizontalScrollUnits), UpdateScrollbars, this.LifetimeManager);
SynchronizeForLifetime(nameof(VerticalScrollUnits), UpdateScrollbars, this.LifetimeManager);
ScrollableContent.Controls.SynchronizeForLifetime(ScrollableControls_Added, (c)=> { }, () => { }, this.LifetimeManager);
}