https://vscodium.com/

It’s so the position: absolute for .leaves works relative to .tree. The implication is that .leaves is a descendant of .tree.

position: absolute looks for the nearest ancestor with a set position in order to determine its own positioning context. Otherwise the absolute positioning would basically be relative to the viewport. If the position: relative was missing, the leaves would be against the bottom edge of the image.

source

edit: I mean .leaves, not .branch