index.html

<!DOCTYPE html>
<meta lang="en">
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">

<main>
  <h1>auto-scroll</h1>
  <p>
    This is just some text to see the scrolling effect.
  </p>
  <p>
    This is just some text to see the scrolling effect.
  </p>
  <p>
    This is just some text to see the scrolling effect.
  </p>
  <p>
    This is just some text to see the scrolling effect.
  </p>
  <p>
    This is just some text to see the scrolling effect.
  </p>
  <p>
    This is just some text to see the scrolling effect.
  </p>
  <p>
    This is just some text to see the scrolling effect.
  </p>
</main>

<style>
  body {
    height: 400vh;
  }

  main {
    height: 100%;
    display: flex;
    flex-direction: column;
    justify-content: space-around;
  }
</style>