.box {
  margin: 10vh auto;
  padding: 2rem 4rem;
  background: hsl(0, 40%, 80%); /* red */
}

@media (min-width: 720px) {
  .box {
    background: hsl(80, 30%, 70%); /* green */
  }
}

@media (min-width: 960px) {
  .box {
    background: hsl(250, 40%, 80%); /* purple */
  }
}