https://www.w3.org/TR/css3-background/#special-backgrounds
This tells me what happens in the context of applying a background, but it doesn’t say why it’s recommended that a background be applied to the <body>.
If the background is specified in the root it spreads throughout the canvas. If the background is declared in the body, while the root is transparent, the background is still treated as if it was specified by the root.
If this preference as mentioned in the spec can be explained in simple terms it will be appreciated.