The first thing I would do here is remove
body from the selector. It is implied. The simple selector will do the same job. Next I would be suspicious of white space that is not engrained in my mind as common syntax.
This will select all elements that are the fourth child of their parent element.
Now if we have mixed element nodes as siblings and nodes are being dynamically added to the 'family' tree, new sibling nodes, that is, and we know that they will never prepend their earlier siblings, we can zero in on a node type.
will select every paragraph that is the fourth child of its parent node.
Likewise we can zero in on the
nth element of type,