Viewport <#document> at [0,0] [0+0+0 800 0+0+0] [0+0+0 600 0+0+0] [BFC] children: not-inline
  BlockContainer <html> at [0,0] [0+0+0 800 0+0+0] [0+0+0 600 0+0+0] [BFC] children: not-inline
    BlockContainer <body> at [0,0] [0+0+0 800 0+0+0] [0+0+0 600 0+0+0] children: not-inline
      BlockContainer <(anonymous)> at [0,0] [0+0+0 800 0+0+0] [0+0+0 0 0+0+0] children: inline
        TextNode <#text> (not painted)
        TextNode <#text> (not painted)
      Box <div> at [0,0] flex-container(column) [0+0+0 800 0+0+0] [0+0+0 18 0+0+0] [FFC] children: not-inline
        BlockContainer <(anonymous)> (not painted) [BFC] children: inline
          TextNode <#text> (not painted)
        BlockContainer <div> at [0,0] flex-item [0+0+0 800 0+0+0] [0+0+0 18 0+0+0] [BFC] children: inline
          frag 0 from TextNode start: 0, length: 1, rect: [0,0 11.5625x18] baseline: 13.796875
              "X"
          TextNode <#text> (not painted)
        BlockContainer <(anonymous)> (not painted) [BFC] children: inline
          TextNode <#text> (not painted)
      BlockContainer <(anonymous)> at [0,18] [0+0+0 800 0+0+0] [0+0+0 0 0+0+0] children: inline
        TextNode <#text> (not painted)

ViewportPaintable (Viewport<#document>) [0,0 800x600]
  PaintableWithLines (BlockContainer<HTML>) [0,0 800x600]
    PaintableWithLines (BlockContainer<BODY>) [0,0 800x600]
      PaintableWithLines (BlockContainer(anonymous)) [0,0 800x0]
      PaintableBox (Box<DIV>) [0,0 800x18]
        PaintableWithLines (BlockContainer<DIV>) [0,0 800x18]
          TextPaintable (TextNode<#text>)
      PaintableWithLines (BlockContainer(anonymous)) [0,18 800x0]

SC for Viewport<#document> [0,0 800x600] [children: 1] (z-index: auto)
 SC for BlockContainer<HTML> [0,0 800x600] [children: 0] (z-index: auto)
