.main-container {
    height: 100%;
    width: 900px;
    margin: 0 auto;
}

.board {
    height: 420px;
    width: 420px;
    margin: 0 auto;
}

.cell {
    width: 140px;
    height: 140px;
    border: 2px solid gray;
    cursor:pointer;
    float:left;
    line-height: 140px;
    text-align: center;
    font-size: 70px;
}

body {
  background-color: #CDD7E1;
  text-align:center;
}