Use overscroll-behavior: contain to prevent a page from scrolling while a is open

~

CSS overscroll-behavior – which I first covered here in 2017 – allows you to control what a browser should do when reaching the boundary of a scrolling area.

For example, if you set it to overscroll-behavior: contain, it will prevent scroll chaining from happening, so that underlying elements don’t scroll.

~

The problem with overscroll-behavior is that it only works when the scroll container is actually scrollable. For example, if you set overscroll-behavior: contain on a <dialog> that doesn’t scroll, then overscroll-behavior won’t do anything. There must at least be 1 pixel of overflow before overscroll-behavior kicks in.

In Chrome 144 this changed, and overscroll-behavior now also works on non-scrollable scroll containers, as intended by the specification. A non-scrollable scroll container gets created when you set overflow: auto but there is no overflow, or when using overflow: hidden.

~

While this change might go unnoticed at first, it unlocks a problem developers have been having for a long time: prevent a page from scrolling when a (modal) <dialog> is open. In Chrome 144+, all it takes is this CSS snippet:

dialog {
	overscroll-behavior: contain;
}
dialog::backdrop {
overflow: hidden;
overscroll-behavior: contain;
}

The key to the code is the overflow: hidden; that you must set on the ::backdrop, as that makes it a (non-scrollable) scroll container.

Try it out in this demo (in Chrome 144+):

(If the page is scrolling underneath the open <dialog>, you are not using Chrome 144+ ;))

I hope that other browser vendors follow suit here, as this solves a real problem developers have been struggling with, and setting overflow: hidden on html as a workaround ain’t exactly cutting it.

For reference, here’s the Gecko/Firefox Bug and the WebKit/Safari Bug.

~