h1 {
    text-align: center;
  }
  
  section {
    margin: 40px;
  }
  
  .box {
    width: 100px;
    height: 100px;
  }
  .is-1 {
    background-color: red;
  }
  
  .is-2 {
    background-color: blue;
  }
  
  .is-3 {
    background-color: green;
  }
  
.grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, 100px);
    justify-content: center;
    grid-gap:1em;
  }