Yes it's xenForo's default style as well as a custom style that I based off of the xenForo style. Everything works, even the sub nav links get they little "..." drop down once it's in narrow width. But the main menu doesn't.
It's responsive, at least it is at the moment. The custom style is what I've developed from the default theme. The default theme never had that functionality to begin with. At least when I upgraded it. You can check it out now and see.