Viewport <#document> at (0,0) content-size 800x600 children: not-inline
  BlockContainer <html> at (0,0) content-size 800x56 [BFC] children: not-inline
    BlockContainer <body> at (8,8) content-size 784x40 children: inline
      frag 0 from Box start: 0, length: 0, rect: [28,28 49.75x0] baseline: 26
      Box <div.button> at (28,28) content-size 49.75x0 flex-container(row) [FFC] children: not-inline
        BlockContainer <(anonymous)> at (28,16.5) content-size 49.75x23 flex-item [BFC] children: inline
          frag 0 from TextNode start: 0, length: 5, rect: [28,16.5 49.75x23] baseline: 17.5
              "Hello"
          TextNode <#text>

ViewportPaintable (Viewport<#document>) [0,0 800x600]
  PaintableWithLines (BlockContainer<HTML>) [0,0 800x56]
    PaintableWithLines (BlockContainer<BODY>) [8,8 784x40]
      PaintableBox (Box<DIV>.button) [8,8 89.75x40]
        PaintableWithLines (BlockContainer(anonymous)) [28,16.5 49.75x23]
          TextPaintable (TextNode<#text>)
