How to blur modal window background in bootstrap?

Question

CMS

Actually, subject.
I now have a simple dark background. How to make a blurry background instead?
I tried to apply the blur filter to the classes of the modal window - the window itself is blurred. but not the background.
https://arturweb.ru/landing/instaby/
Modal windows are on the "registration" and "login" buttons.

Answer 1

Blur should be applied to.modal-backdrop.in