Background color for single menu item

Hello everybody,
How can I give a background color to individual menu items?

The site is FantaSvaimec.it, at the moment everything is ready to enable MMM but these details are missing.

To be clear, as in the image below, done with CSS customization of the Colormag theme

https://drive.google.com/file/d/1xKy94EacH6mh5-Ox0_HjF1iPBYkUdqIa/view?usp=sharing

Thanks