Update: I don't understand why you think the host can, or will help you.
You're going to have to do research online to learn more about firewalls, and you're going to have to become a lot more intelligent. The host's job is to host whatever you have. I don't think the host will, or can help you in this manner. I have used different hosting companies, and now I host my own website(s). Control is something that you're going to need, but having a lot of control is not easy to manage.
I don't know if you realize how difficult your question is. HTML, and CSS has nothing to do with what you want to know. You are going to have to learn about firewalls. What you want to know is going to take time, for you to learn it. I know it's possible to restrict individual networks, and this is easy to do in comparison to almost every country. Unfortunately I don't know how a firewall should be configured to restrict access to almost every country. Well now at least you have an idea of what to look into, so I hope I was able to help you a little bit.