Main menu in proj.org in mobile phone not shown

[jjimenezshaw]

This issue is about the documentation in https://proj.org/

I just opened it today in my mobile phone, and the "hamburger menu" in the top left corner (three horizontal bars) does not do anything. If I remember correctly, it was opening the main menu.

It is reproducible (in my Ubuntu) in chrome ("device toolbar") and firefox ("responsive design mode").