overscroll-behavior-block

/* キーワード値 */
overscroll-behavior-block: auto; /* 既定値 */
overscroll-behavior-block: contain;
overscroll-behavior-block: none;
/* グローバル値 */
overscroll-behavior-block: inherit;
overscroll-behavior-block: initial;
overscroll-behavior-block: revert;
overscroll-behavior-block: revert-layer;
overscroll-behavior-block: unset;

<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>

main {
  height: 3000px;
  width: 500px;
  background-color: white;
  background-image: repeating-linear-gradient(
    to bottom,
    transparent 0px,
    transparent 19px,
    rgb(0 0 0 / 50%) 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,
    transparent 0px,
    transparent 19px,
    rgb(0 0 0 / 50%) 20px
  );
}
p {
  padding: 10px;
  background-color: rgb(255 0 0 / 50%);
  margin: 0;
  width: 340px;
  position: relative;
  top: 10px;
  left: 10px;
}