Indentation Problem with Navigation Bar

So, I am new to coding and I am currently practicing with Technical Documentation project on Responsive Web Design certification. So, what I am trying to do here is typing the exact code from the example one by one to at least get the feeling of how it’s done before making the lines of codes of my own.

At first the result seems fine. But then, the moment I click the navigation bar, the body of the page suddenly got indented to the left, beyond even the right border of the navigation bar. I am sorry that I cannot provide any screenshots. The forum does not seem to allow new users like myself to do that.

Anybody might know what I did wrong?

Also, I would be very happy to provide some screenshots and codes that I typed, but the forum does not allow me to do either. So, I do not know how I am supposed to ask anything in this forum. If anyone has solution for this problem as well, I would like to hear it as well. Thank you in advance.

totally impossible to have an idea of what’s happening without seeing the code

you need to include the link to your pen
you could partecipate a bit in the forum to unlock the links, or you could use Preformatted text, surroudnign the link with backticks or just using the </> button in the text editor

Here is the link to my codepen: I thought link was not allowed so I did not post it earlier. Thanks for the reply.