in css, there are a huge multitude of ways to select the same set of elements.
For eg. Here are some valid methods: ul > li > a ul li a nav > ul > li > a nav a ul a li a body li a
The test cannot realistically accept all valid answers for each step. It would not be possible for the developers to work out all the ways someone can answer correctly.
So that’s why your code didn’t work. Someone just didn’t think of this as a possible answer.