style.css

body {
    position: relative;
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    width: 100vw;
    height: 100vh;
    background-color: #676767;
}

#play_btn_human {
    position: absolute;
    top: 15vh;
    left: 45vw;
    width: 80px;
    height: 50px;
    transform: translate(-50%, -50%);
    color: white;
    background-color: black;
    border: 0px;
    border-radius: 5px;
}

#play_btn_ai {
    position: absolute;
    top: 15vh;
    left: 55vw;
    width: 80px;
    height: 50px;
    transform: translate(-50%, -50%);
    color: black;
    background-color: white;
    border: 0px;
    border-radius: 5px;
}

#board {
    position: absolute;
    width: 60vh;
    height: 60vh;
    top: 50vh;
    left: 50vw;
    transform: translate(-50%, -50%);
    /* border: 1px solid black; */
    background-image: url("./board.png");
    background-repeat: no-repeat;
    background-position: center;
    background-size: 91% 91%;
}

.row {
    position: relative;
    width: 100%;
    height: 9%;
    display: flex;
    flex-direction: row;
    justify-content: space-around;
    align-items: center;
}

.cell {
    position: relative;
    width: 5%;
    height: 3vh;
    margin: 5px;
    /* border: 1px solid red; */
    border-radius: 50%;
}

.black {
    background-color: black;
}

.white {
    background-color: white;
}

#msg-box {
    position: absolute;
    left: 50%;
    top: 85%;
    transform: translate(-50%, -50%);
    width: 400px;
    height: 150px;
    text-align: center;
    line-height: 150px;
    /* border: 1px solid black; */
    font-size: 1.8em;
    color: #8CEA00;
    font-family: 'Press Start 2P', cursive;
}