How to restrict a portrait view if I'm building a landscape course?

If your course is meant for mobile users, consider why you’re forcing landscape mode—most learners are comfortable with portrait. Instead of restricting orientation, design a responsive layout that works well in both views for better accessibility.

Why build it in responsive then?  Unless you have a crying need to have people view the content on a mobile phone, you are probably better off just to use normal project HTML5.