With opacity:
AccumulatedVisualContext Tree:
  [0] transform=[1,0,0,1,0,0] origin=(0,0) (ViewportPaintable(Viewport<#document>))
    [1] scroll (PaintableWithLines(BlockContainer<PRE>#out))
      [2] effects=[opacity=0.5] (InlinePaintable(InlineNode<SPAN>#target))

DisplayList:
SaveLayer@0
  CompositorWheelHitTestTarget@0 target_scroll_node_index=0 rect=[0,0 800x600]
  CompositorWheelHitTestTarget@1 target_scroll_node_index=0 rect=[0,0 800x111]
  CompositorWheelHitTestTarget@1 target_scroll_node_index=0 rect=[8,8 784x90]
  CompositorWheelHitTestTarget@1 target_scroll_node_index=0 rect=[8,8 100x64]
  CompositorWheelHitTestTarget@1 target_scroll_node_index=0 rect=[8,85 784x13]
  DrawGlyphRun@1 rect=[8,85 83x13] translation=[8,95.390625] color=rgb(0, 0, 0)
  CompositorWheelHitTestTarget@2 target_scroll_node_index=0 rect=[8,8 81.21875x64]
  FillRect@2 rect=[8,8 81x16] color=rgb(255, 165, 0)
  FillRect@2 rect=[8,24 47x16] color=rgb(255, 165, 0)
  FillRect@2 rect=[8,40 60x16] color=rgb(255, 165, 0)
  FillRect@2 rect=[8,56 36x16] color=rgb(255, 165, 0)
  DrawGlyphRun@2 rect=[8,8 82x16] translation=[8,20.796875] color=rgb(0, 0, 0)
  DrawGlyphRun@2 rect=[8,24 48x16] translation=[8,36.796875] color=rgb(0, 0, 0)
  DrawGlyphRun@2 rect=[8,40 60x16] translation=[8,52.796875] color=rgb(0, 0, 0)
  DrawGlyphRun@2 rect=[8,56 37x16] translation=[8,68.796875] color=rgb(0, 0, 0)
Restore@0

Without opacity:
AccumulatedVisualContext Tree:
  [0] transform=[1,0,0,1,0,0] origin=(0,0) (ViewportPaintable(Viewport<#document>))
    [1] scroll (PaintableWithLines(BlockContainer<PRE>#out))

DisplayList:
SaveLayer@0
  CompositorWheelHitTestTarget@0 target_scroll_node_index=0 rect=[0,0 800x600]
  CompositorWheelHitTestTarget@1 target_scroll_node_index=0 rect=[0,0 800x436]
  CompositorWheelHitTestTarget@1 target_scroll_node_index=0 rect=[8,8 784x415]
  CompositorWheelHitTestTarget@1 target_scroll_node_index=0 rect=[8,8 100x64]
  CompositorWheelHitTestTarget@1 target_scroll_node_index=0 rect=[8,85 784x338]
  CompositorWheelHitTestTarget@1 target_scroll_node_index=0 rect=[8,8 81.21875x64]
  FillRect@1 rect=[8,8 81x16] color=rgb(255, 165, 0)
  FillRect@1 rect=[8,24 47x16] color=rgb(255, 165, 0)
  FillRect@1 rect=[8,40 60x16] color=rgb(255, 165, 0)
  FillRect@1 rect=[8,56 36x16] color=rgb(255, 165, 0)
  DrawGlyphRun@1 rect=[8,8 82x16] translation=[8,20.796875] color=rgb(0, 0, 0)
  DrawGlyphRun@1 rect=[8,24 48x16] translation=[8,36.796875] color=rgb(0, 0, 0)
  DrawGlyphRun@1 rect=[8,40 60x16] translation=[8,52.796875] color=rgb(0, 0, 0)
  DrawGlyphRun@1 rect=[8,56 37x16] translation=[8,68.796875] color=rgb(0, 0, 0)
  DrawGlyphRun@1 rect=[8,85 83x13] translation=[8,95.390625] color=rgb(0, 0, 0)
  DrawGlyphRun@1 rect=[8,98 214x13] translation=[8,108.390625] color=rgb(0, 0, 0)
  DrawGlyphRun@1 rect=[8,111 546x13] translation=[8,121.390625] color=rgb(0, 0, 0)
  DrawGlyphRun@1 rect=[8,124 404x13] translation=[8,134.39062] color=rgb(0, 0, 0)
  DrawGlyphRun@1 rect=[8,137 479x13] translation=[8,147.39062] color=rgb(0, 0, 0)
  DrawGlyphRun@1 rect=[8,163 74x13] translation=[8,173.39062] color=rgb(0, 0, 0)
  DrawGlyphRun@1 rect=[8,176 85x13] translation=[8,186.39062] color=rgb(0, 0, 0)
  DrawGlyphRun@1 rect=[8,189 551x13] translation=[8,199.39062] color=rgb(0, 0, 0)
  DrawGlyphRun@1 rect=[8,202 541x13] translation=[8,212.39062] color=rgb(0, 0, 0)
  DrawGlyphRun@1 rect=[8,215 538x13] translation=[8,225.39062] color=rgb(0, 0, 0)
  DrawGlyphRun@1 rect=[8,228 536x13] translation=[8,238.39062] color=rgb(0, 0, 0)
  DrawGlyphRun@1 rect=[8,241 542x13] translation=[8,251.39062] color=rgb(0, 0, 0)
  DrawGlyphRun@1 rect=[8,254 532x13] translation=[8,264.39062] color=rgb(0, 0, 0)
  DrawGlyphRun@1 rect=[8,267 567x13] translation=[8,277.39062] color=rgb(0, 0, 0)
  DrawGlyphRun@1 rect=[8,280 337x13] translation=[8,290.39062] color=rgb(0, 0, 0)
  DrawGlyphRun@1 rect=[8,293 343x13] translation=[8,303.39062] color=rgb(0, 0, 0)
  DrawGlyphRun@1 rect=[8,306 345x13] translation=[8,316.39062] color=rgb(0, 0, 0)
  DrawGlyphRun@1 rect=[8,319 345x13] translation=[8,329.39062] color=rgb(0, 0, 0)
  DrawGlyphRun@1 rect=[8,332 527x13] translation=[8,342.39062] color=rgb(0, 0, 0)
  DrawGlyphRun@1 rect=[8,345 532x13] translation=[8,355.39062] color=rgb(0, 0, 0)
  DrawGlyphRun@1 rect=[8,358 533x13] translation=[8,368.39062] color=rgb(0, 0, 0)
  DrawGlyphRun@1 rect=[8,371 533x13] translation=[8,381.39062] color=rgb(0, 0, 0)
  DrawGlyphRun@1 rect=[8,384 72x13] translation=[8,394.39062] color=rgb(0, 0, 0)
  DrawGlyphRun@1 rect=[8,410 105x13] translation=[8,420.39062] color=rgb(0, 0, 0)
Restore@0

