Page scale in the ZEN template

Good day to everyone.

While going through the theming lessons, I encountered a problem.

The issue appeared almost immediately. After installing the ZEN theme, creating its sub-theme, and activating the template, I noticed that the scale of my page does not match what is shown in the tutorial video; my template is significantly larger, and when I zoom in or out using the scroll, all the fields shift. When I try to comment out max-width to stretch it across the entire page as indicated, nothing happens.

As a result, I can't continue with the layout because I can't even center the site title. I am unable to make the theme look the same as in the video. Could you please advise me on what the problem is and how it can be resolved?

Thank you!