AccumulatedVisualContext Tree:
  [0] transform=[1,0,0,1,0,0] origin=(0,0) (ViewportPaintable(Viewport<#document>))
    [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 800x53]
  CompositorWheelHitTestTarget@1 target_scroll_frame_index=0 rect=[8,8 784x32]
  CompositorWheelHitTestTarget@1 target_scroll_frame_index=0 rect=[8,8 784x32]
  CompositorWheelHitTestTarget@1 target_scroll_frame_index=0 rect=[8,8 32x32]
  DrawCanvas@1 dst_rect=[8,8 32x32]
Restore@0