This builder does not make responsive websites. If it can be done via code, I have not seen that and we wouldn't be able to give you the code for it. I would recommend rebuilding your site in our newer builder Website Builder. This builder DOES create responsive sites without having to add code. It is also generally more updated and modern and created better websites. You would just need to add a new site on your account, and it will automatically be created in the newer builder.