#div0 {
    width: 100%;
    height: 500px;
  }

  #div0 div {
    float: left;
    height: 100px
  }

  #div0 div:nth-child(1) {
    background-color: aqua;
  }

  #div0 div:nth-child(2) {
    background-color: red;
  }

  #div0 div:nth-child(3) {
    background-color: green;
  }