Viewport <#document> at (0,0) content-size 800x600 children: not-inline
  BlockContainer <html> at (0,0) content-size 800x200 [BFC] children: not-inline
    Box <body> at (0,0) content-size 400x200 flex-container(column) [FFC] children: not-inline
      ImageBox <img> at (0,0) content-size 400x200 flex-item children: not-inline

ViewportPaintable (Viewport<#document>) [0,0 800x600]
  PaintableWithLines (BlockContainer<HTML>) [0,0 800x200]
    PaintableBox (Box<BODY>) [0,0 400x200]
      ImagePaintable (ImageBox<IMG>) [0,0 400x200]
