Viewport <#document> at (0,0) content-size 800x600 children: not-inline
  BlockContainer <html> at (0,0) content-size 800x58 [BFC] children: not-inline
    BlockContainer <body> at (8,8) content-size 784x42 children: inline
      frag 0 from BlockContainer start: 0, length: 0, rect: [29,29 0x0] baseline: 42
      BlockContainer <button> at (29,29) content-size 0x0 positioned inline-block [BFC] children: not-inline
        BlockContainer <(anonymous)> at (29,29) content-size 0x0 flex-container(column) [FFC] children: not-inline
          BlockContainer <(anonymous)> at (29,29) content-size 0x0 flex-item [BFC] children: not-inline
            BlockContainer <(anonymous)> at (9,9) content-size 40x40 positioned [BFC] children: inline
              TextNode <#text>
      TextNode <#text>

ViewportPaintable (Viewport<#document>) [0,0 800x600]
  PaintableWithLines (BlockContainer<HTML>) [0,0 800x58]
    PaintableWithLines (BlockContainer<BODY>) [8,8 784x42]
      PaintableWithLines (BlockContainer<BUTTON>) [8,8 42x42]
        PaintableWithLines (BlockContainer(anonymous)) [29,29 0x0]
          PaintableWithLines (BlockContainer(anonymous)) [29,29 0x0]
            PaintableWithLines (BlockContainer(anonymous)) [9,9 40x40]
