AccumulatedVisualContext Tree:
  [1] scroll_frame_id=1 (PaintableWithLines(BlockContainer<PRE>#out))

DisplayList:
SaveLayer@0
  CompositorWheelHitTestTarget@0 target_scroll_frame_index=0 rect=[0,0 800x600]
  CompositorWheelHitTestTarget@1 target_scroll_frame_index=0 rect=[0,0 800x41]
  CompositorWheelHitTestTarget@1 target_scroll_frame_index=0 rect=[8,8 784x20]
  CompositorWheelHitTestTarget@1 target_scroll_frame_index=0 rect=[8,8 100x20]
  FillRect@1 rect=[8,8 1x18] color=rgb(0, 0, 0)
  FillPath@1 path_bounding_rect=[6,6 104x24]
Restore@0