The element is not displayed on wordpress, what can be done?

Question

css

Hello.
For the site it was necessary to make an off-canvas menu.
When you zoom in / out of the browser, it works, but on a mobile phone it is not visible, what can be done?
At the same time, it is in place, it is simply not visible (links are clicked, transitions are made).

how it looks on the computer


how it looks on the mobile


When the browser width on the computer is about 340, everything works fine, media queries work.
But on the phone, the menu is displayed as seen in the second screen.

Answer 1

Isn't it about CSS?
Behavior, depending on the resolution, is written in media screen blocks