Why is it that when I set a background for the body, the entire page is painted even though the body has a much smaller height?

Question

css

Answer 1

This is a special exception for backward compatibility
https://drafts.csswg.org/css-backgrounds-3/#body-b...
For documents whose root element is an HTML HTML element or an XHTML html element [HTML]: if the computed value of background-image on the root element is none and its background-color is transparent, user agents must instead propagate the computed values ​​of the background properties from that element's first HTML BODY or XHTML body child element. The used values ​​of that BODY element's background properties are their initial values, and the propagated values ​​are treated as if they were specified on the root element.