AccumulatedVisualContext Tree:
  [1] scroll_frame_id=1 (PaintableWithLines(BlockContainer<PRE>#out))
    [2] clip=[8,8 200x200]
      [3] effects=[opacity=0.5]
        [4] transform=[1,0,0,1,20,20] origin=(8,8) (SVGPathPaintable(SVGGeometryBox<rect>))

DisplayList:
SaveLayer@0
  CompositorWheelHitTestTarget@0 target_scroll_frame_index=0 rect=[0,0 800x600]
  CompositorWheelHitTestTarget@1 target_scroll_frame_index=0 rect=[0,0 800x221]
  CompositorWheelHitTestTarget@1 target_scroll_frame_index=0 rect=[8,8 784x200]
  CompositorWheelHitTestTarget@1 target_scroll_frame_index=0 rect=[8,8 784x200]
  CompositorWheelHitTestTarget@1 target_scroll_frame_index=0 rect=[8,8 200x200]
  FillPath@4 path_bounding_rect=[8,8 100x100]
Restore@0