How to make a backdrop in a modal form?

Question

Bootstrap

Hello. And how to make a backdrop (rear translucent background) in a modal window. I will not display the window with jquery. I searched in the developer tools where this background changes after clicking on the button in the examples, but I did not find it.
Example

Answer 1

Well, in general, this script adds https://c2n.me/3S6y0ar
You can view it in the browser through the developer tools.
Your example with connected scripts - https://jsfiddle.net/kreoTech/qewrdcn7/1/