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: