Not all of the html is defined in the css, only the important elements are. The extra code you see shows up because it is the end result of the outputted code in Genesis and the Child theme template file. We could define all of the classes if we wanted too, but its not necessary to do so if its not needed.
You most likely won’t have to add the ones that aren’t defined, but it won’t hurt if you left it there. It’s nothing to worry about, just add the code that you need and you should be fine.