Slider menu causes Problems

Question

Heii
For homework I have to create a website. I'm in the process of making a drop down menu. The problem is that the menu on the mobile website is the same as on the desktop website.I myself don't know why the menu of the desktop version is not replaced by the menu of the mobile version
Codeblock:
Name: submenu a
Codeline: 218
https://code.sololearn.com/WPhM9yZxHvAp/?ref=app

Answer 1

Now on the desktop, the entire menu is vertical in one column, and on the mobile in two columns. What do you expect the result to be?