I have logged in and checked your header which seems to be perfect already on desktop screens. The problem is that as soon as you view the site on a smaller screen, the header is not responsive. As to what @christian has already said that “the header will be responsive if the user chooses it to be responsive”. This means that your header is designed for desktop screens. What you need to do now is to insert another bar and design your header specifically for the smaller screens. You can show or hide the corresponding bars in specific screen size by utilizing the “Hide During Breakpoints” option. To learn more about this, you can check it here:
As for the elements, the navigation inline element is only good for desktop screens. For smaller screens, you will have to add navigation layered, navigation modal, or navigation collapsed element.
Hope this makes sense to you.