<section>
  <div style="background:#CCFFFF">A</div>
  <div style="background:#FFCCFF">B</div>
  <div style="background:#FFFFCC">C</div>
  <div style="background:#FFCCCC">D</div>
</section>

:root{
  /*要素の数*/
 --box_cont: 4;
}

@keyframes scroll_anim {
  from {
    transform: translate(0%, 0%);
  }
  to {
    transform: translate(calc(-100% * calc(var(--box_cont) - 1)), 0%);
  }
}

body {
  height: calc(100svh * var(--box_cont));
}
section {
  display: flex;
  width: 100%;
  overflow: hidden;
  position: fixed;
  top: 0;
  left: 0;
}
section > div {
  width: 100%;
  height: 100svh;
  font-size: 3rem;
  font-weight: bold;
  display: flex;
  flex-shrink: 0;
  align-items: center;
  justify-content: center;
  transform-origin: left;
  animation: scroll_anim linear;
  animation-timeline: scroll(root);
}