#board{
    display: flex;
    flex-wrap: wrap;
    width: 640px;
    height: 640px;
    border:1px solid black;
    background-color: #fff;

  }
  
   .esquare:nth-of-type(2n){
    background-color: #000;
  }
  .osquare:nth-of-type(2n+1){
    background-color: #000;
  }