How to make the background blurry?

Question

css

Hello everyone, how can I set the background "blurry" roughly speaking so that it does not take a square shape, and no matter how the edges of the element in which to be located seem to be. Here is an example. The screenshot shows that there is a parent with one color, and a child with the same but more transparent color, but at the same time the child does not seem to touch the edges and due to this it seems to be "blurry"

Answer 1

to be honest, they wrote such a bereberd that they already put balls on their foreheads when they read

"vaguely" roughly speaking so that it does not take a square shape

blur effect? it is purely logically clear that the background in one color this bagel in another has shadows.

no matter how the edges of the element in which to be

it’s generally how to understand, maybe you need to be in some kind of trance effect in order to begin to understand what you wrote.