Thank you once again for the answer.
I figured out that the problem was Nginx. See here: https://stackoverflow.com/questions/43597920/moodle-3-0-css-and-javascript-dont-load-requests-to-nginx-arent-compatible
I figured out that the problem was Nginx. See here: https://stackoverflow.com/questions/43597920/moodle-3-0-css-and-javascript-dont-load-requests-to-nginx-arent-compatible