How do I stop scrolling of page when overlay div is visible?

[pioleoberb]

The page I'm working with sometimes displays a modal layover with a div (position: fixed) > div (position: relative; width/height: 100%) > div (position: absolute; left/right: 50%).Both on mobile devices and on Chrome/Safari on the desktop, swiping still scrolls the page behind the layover. Can I prevent this with CSS, and, if so, how?