Why aren't files from the static folder included in a Flask application?

Question

Flask

Learn Flask from YouTube videos. And there is one problem that I can’t solve in any way - files (css, js, images) from the static folder via url_for. At the moment I have exactly the same code as in this video , but js and css files are not included, although no errors are issued in debugging mode. And this is the third author in whose lessons I dwell on the moment of connecting static files. From which I concluded that the problem is in the permission to access files (and definitely not my typos). Because the styles don't change, the script doesn't work. But url_forit works great when redirecting to other routes. What could be the problem?
PS I'm doing all this on a macbook

Answer 1

The problem is learning from the video, read the textbook.