<length>

An outset from the inline start edge of the scroll container.

scroll-margin-inline-start = 
  <length>  

This example implements something very similar to the interactive example above, except that here we'll explain to you how it's implemented.

The aim here is to create four horizontally-scrolling blocks, the second and third of which snap into place, near but not quite at the left of each block.

HTML

The HTML that represents the blocks is very simple:

<div class="scroller">
  <div>1</div>
  <div>2</div>
  <div>3</div>
  <div>4</div>
</div>

CSS

Let's walk through the CSS. The outer container is styled like this:

.scroller {
  text-align: left;
  width: 250px;
  height: 250px;
  overflow-x: scroll;
  display: flex;
  box-sizing: border-box;
  border: 1px solid #000;
  scroll-snap-type: x mandatory;
}

The main parts relevant to the scroll snapping are overflow-x: scroll, which makes sure the contents will scroll and not be hidden, and scroll-snap-type: x mandatory, which dictates that scroll snapping must occur along the horizontal axis, and the scrolling will always come to rest on a snap point.

The child elements are styled as follows:

.scroller > div {
  flex: 0 0 250px;
  width: 250px;
  background-color: #663399;
  color: #fff;
  font-size: 30px;
  display: flex;
  align-items: center;
  justify-content: center;
  scroll-snap-align: start;
}

.scroller > div:nth-child(2n) {
  background-color: #fff;
  color: #663399;
}

The most relevant part here is scroll-snap-align: start, which specifies that the left-hand edges (the "starts" along the x axis, in our case) are the designated snap points.

Last of all we specify the scroll margin-values, a different one for the second and third child elements:

.scroller > div:nth-child(2) {
  scroll-margin-inline-start: 1rem;
}

.scroller > div:nth-child(3) {
  scroll-margin-inline-start: 2rem;
}

This means that when scrolling past the middle child elements, the scrolling will snap to 1rem outside the inline start edge of the second <div>, and 2rems outside the inline start edge of the third <div>.

Result

Try it for yourself:

• CSS Scroll Snap
• Well-Controlled Scrolling with CSS Scroll Snap