div {
  width: 100cqi;
  @container (min-width: 640px) {
    width: 50cqi;
  }
}
main{
  container-type: inline-size;
  display: flex;
  flex-wrap: wrap;
}
@layer demo {
  div {
    border: medium solid black;
    height: 200px;
    box-sizing: border-box;
    display: inline-block;
  }
  body {
    display: grid;
    grid-template-columns: 250px 1fr;
    gap: 1em;
  }
  nav{
    background: teal;
  }
}