<main>
  <aside></aside>
  <section></section>
</main>

<main>
  <aside style="grid-column-end: -2;"></aside>
  <section></section>
</main>

main {
  display: grid;
  grid-template-columns: 1fr;
  grid-auto-flow: column;
  height: 100px;
  gap: 20px;
  border: 5px solid;
  margin: 10px;
}
section {
  min-width: 100px;
  background: red;
}
aside {
  min-width: 100px;
  background: blue;
}