Vanilla JavaScript menu

A simple menu, usually taken from some existing library, but I have built it from scratch using only vanilla JavaScript, HTML and CSS.

Features:

• opens when clicking on the element
• menu-item color change on hover - color stays changed when the item is selected (menu open)
• switches between the submenus
• second click on the currently opened item closes the menu
• "Esc" and a click outside the menu closes the entire menu
• responsive - from 500px changes to hamburger with the same functionality for submenus

The menu-items should be added as the list items to the list, according to the following template:

The menus should be added as:

with level-2 subitems (which need to be linked to the respective targets).