Why does the content shift when opening a modal window?

Question

JavaScript

when opening a modal window on the site, the main content of the site is shifted to the left by 23-35px (except for the fixed header). With what it can be connected and what methods of the decision?

Answer 1

Write in css
.modal-open{overflow-y: scroll;}
or
.modal-open{overflow-y: visible;}

Answer 2

You lose scroll.