純粋な CSS で複数のスティッキー要素を積み重ねることはできますか?

#sticky .sticky-1,
#sticky .sticky-2
{
  position: sticky;
}
#sticky .sticky-1
{
  top: 1em;
  z-index: 1;
}
#sticky .sticky-2
{
  top: 2em;
  z-index: 1;
}

<code class="html"><div id="container">
  <article id="sticky">
    <header>
    </header>
    <main>
      <h1 class="sticky-1">Sticky heading</h1 >
      <p>here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. Some copy goes here. </p>
    </main>
    <section>
      <h2 class="sticky-2">Both headings should stick at the same time.</h2 ></code>