Don't resize the body when you open a modal

block-scroll.css

/* the page should not change width as content is loaded */
body {
  overflow-y: scroll;
}

/* block scrolling without losing the scroll bar and shifting the page */
/* add this class when a modal is open */
body.block-scroll {
  overflow: hidden;
  overflow-y: scroll !important;
  position: fixed;
  width: 100%;
}