style.css

td{
    border: 2px solid #333; /* giving a border to each cell*/
    height: 100px;
    width: 100px;
    text-align: center;
    vertical-align: middle;
    font-size: 70px;
    cursor: pointer;
}

table{
    border-collapse: collapse; /* removing the unwanted space between the cells*/
    position: absolute;
    left: 50%;
    margin-left: -155px;
    top: 50px;
}

table tr:first-child td{
    border-top: 0; /* removing upper border from the 1st table row*/
}

table tr:last-child td{
    border-bottom: 0; /* removing lower border from the last table row*/
}
table tr td:first-child{
    border-left: 0; /* removing left border from the 1st table column*/
}
table tr td:last-child{
    border-right: 0; /* removing right border from the last table column*/
}

.endgame{  /* styling the modal that pops after game finishes*/
    display: none;
    width: 200px;
    top: 120px;
    background-color: rgba(16, 24, 143, 0.8);
    position: absolute;
    left: 50%;
    margin-left: -100px;
    padding-top: 0px;
    text-align: center;
    border-radius: 5px;
    color: white;
    font-size: 2em;
}


.playAgainbtn{  /* styling play again button*/
    position: absolute;
    left: 46.75%;
    top: 55%;
    background-color: green;
    color: white;
    border: 10px solid green;
    border-radius: 5px;
    cursor: pointer;
}