XF 1.5 How to make theme mobile compatible?


Hiya, I am currently trying to make the current theme I have on my Xenforo page mobile compatible, I have responsive design enabled in ACP, but it still doesn't work, for example when you try to scroll out on mobile, it creates a white box instead of extending the page. I have image attached below:
If someone could explain how to make this theme mobile compatible, I would very much appreciate it!