Test that overlapped, nested and clipped scrollable areas are correctly targeted.

case 1: Scrollable 1 
case 2: 
case 3: Scrollable 3 
case 4: Scrollable 6 
case 5: Scrollable 8 
case 6: Scrollable 9 
case 7: Scrollable 12 
case 8: Scrollable 13 
case 9: Scrollable 15 
case 10: 
case 11: