Viewport <#document> at (0,0) content-size 800x600 children: not-inline
  BlockContainer <html> at (0,0) content-size 800x600 [BFC] children: not-inline
    BlockContainer <body> at (8,8) content-size 784x17 children: inline
      frag 0 from BlockContainer start: 0, length: 0, rect: [13,19 0x0] baseline: 4
      BlockContainer <button> at (13,19) content-size 0x0 inline-block [BFC] children: not-inline
        BlockContainer <(anonymous)> at (13,19) content-size 0x0 flex-container(column) [FFC] children: not-inline
          BlockContainer <(anonymous)> at (13,19) content-size 0x0 [BFC] children: not-inline

ViewportPaintable (Viewport<#document>) [0,0 800x600]
  PaintableWithLines (BlockContainer<HTML>) [0,0 800x600]
    PaintableWithLines (BlockContainer<BODY>) [8,8 784x17]
      PaintableWithLines (BlockContainer<BUTTON>) [8,17 10x4]
        PaintableWithLines (BlockContainer(anonymous)) [13,19 0x0]
          PaintableWithLines (BlockContainer(anonymous)) [13,19 0x0]
