Within this module it states “A descendant combinator is used to target elements matched by the second selector if they are nested within an ancestor element that matches the first selector. An ancestor can be a parent element or a parent’s parent.”
I’m not sure about anyone else but the wording makes it seem like this will ONLY apply to elements that are nested either directly or only one layer below/above. This is not the case since CSS typically does not care how deep the nesting actually goes unless you break the structural chain of command within the HTML file. In theory you could have a selector combinator that spans the entire document and as long as the chain of command within HTML is not broken then it will still work.