How made background mask when mobile-menu opened?

How made background mask when mobile-menu opened? For example like in google gmail app

Hello Vitalii,

I have checked your site and I see the similar menu as on the google gmail app. Would you please explain us in more details what exactly do you want. With screenshots if possible.

Hello Viktor

Attachment 2367Attachment 2368

Hello Vitalii,

I can try to add this mask but you need to create a new ticket.