/* Keyword values */
overscroll-behavior-block: auto; /* default */
overscroll-behavior-block: contain;
overscroll-behavior-block: none;

/* Global values */
overscroll-behavior-block: inherit;
overscroll-behavior-block: initial;
overscroll-behavior-block: revert;
overscroll-behavior-block: revert-layer;
overscroll-behavior-block: unset;

The overscroll-behavior-block property is specified as a keyword chosen from the list of values below.

auto

The default scroll overflow behavior occurs as normal.

contain

Default scroll overflow behavior (e.g., "bounce" effects) is observed inside the element where this value is set. However, no scroll chaining occurs on neighboring scrolling areas; the underlying elements will not scroll. The contain value disables native browser navigation, including the vertical pull-to-refresh gesture and horizontal swipe navigation.

none

No scroll chaining occurs to neighboring scrolling areas, and default scroll overflow behavior is prevented.

overscroll-behavior-block = 
  contain  |
  none     |
  auto     

In this demo we have two block-level boxes, one inside the other. The outer box has a large height set on it so the page will scroll vertically. The inner box has a small width (and height) set on it so it sits comfortably inside the viewport, but its content is given a large height so it will also scroll vertically.

By default, when the inner box is scrolled and a scroll boundary is reached, the whole page will begin to scroll, which is probably not what we want. To avoid this happening in the block direction, we've set overscroll-behavior-block: contain on the inner box.

HTML

<main>
  <div>
    <div>
      <p>
        <code>overscroll-behavior-block</code> has been used to make it so that
        when the scroll boundaries of the yellow inner box are reached, the
        whole page does not begin to scroll.
      </p>
    </div>
  </div>
</main>

CSS

main {
  height: 3000px;
  width: 500px;
  background-color: white;
  background-image: repeating-linear-gradient(
    to bottom,
    rgba(0, 0, 0, 0) 0px,
    rgba(0, 0, 0, 0) 19px,
    rgba(0, 0, 0, 0.5) 20px
  );
}

main > div {
  height: 300px;
  width: 400px;
  overflow: auto;
  position: relative;
  top: 50px;
  left: 50px;
  overscroll-behavior-block: contain;
}

div > div {
  height: 1500px;
  width: 100%;
  background-color: yellow;
  background-image: repeating-linear-gradient(
    to bottom,
    rgba(0, 0, 0, 0) 0px,
    rgba(0, 0, 0, 0) 19px,
    rgba(0, 0, 0, 0.5) 20px
  );
}

p {
  padding: 10px;
  background-color: rgba(255, 0, 0, 0.5);
  margin: 0;
  width: 340px;
  position: relative;
  top: 10px;
  left: 10px;
}

Result

• Take control of your scroll: customizing pull-to-refresh and overflow effects