index.css

.parentTop {
    display: flex;
    align-items: center;
    justify-content: center;
}

.gridTop {
    border-color: "#f44336";
    border: '1px solid red';
    display: flex;
    flex-direction: column;
}

.lightBackground {
    background-color: 00FFFF
}

.columnsStyle {
    display: flex;
    flex-direction: column;
}

.rowStyle {
    display: flex;
}

.darkBackground {
    background-color: F0FFFF
}

.box {
    width: 150;
    height: 150;
    cursor: pointer;
    display: flex;
    justify-content: center;
    align-items: center;
}

.header {
    display: flex;
    align-items: center;
    justify-content: center;
    margin-bottom: 100px;
}

.cross {
    color: #f90;
    font-size: 2.5em;
    border-radius: 5px;
    line-height: 100px;
}

.playButton {
    text-align: center;
    left: 50%;
    padding-top: 30px;
}

.gameEventModal {
    display: block;
    z-index: 1;
    text-align: center;
    padding-top: 20%;
    overflow: auto;
    background-color: rgba(0, 0, 0, 0.4);
    width: 100%;
    height: 100%;
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
}

.gameEventModalContent {
    background-color: white;
    margin: auto;
    padding: 20px;
    border: none;
    width: 30%;
}

.winnerModal{
    display: none;
    z-index: 1;
    text-align: center;
    padding-top: 20%;
    overflow: auto;
    background-color: rgba(0, 0, 0, 0.4);
    width: 100%;
    height: 100%;
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
}

.winnerModalContent{
    background-color: white;
    margin: auto;
    padding: 20px;
    border: none;
    width: 30%;
}

button {
    background: rgb(106, 26, 171);
    color: white;
    font-size: 100%;
    border: none;
    position: relative;
    height: 10%;
    width: 30%;
    cursor: pointer;
    transition: 800ms ease all;
    outline: none;
}

button:hover {
    background: white;
    color: rgb(77, 26, 171);
}

.loader {
    display: block;
    z-index: 1;
    text-align: center;
    border: 5px solid #f3f3f3;
    border-top: 5px solid #3498db;
    border-radius: 50%;
    width: 50px;
    height: 50px;
    position: fixed;
    opacity: .5;
    animation: spin 2s linear infinite;
    left: 50%;
    top: 50%;
    transform: translate(-50%, -50%);
}

@keyframes spin {
    0% {
        transform: rotate(0deg);
    }
    100% {
        transform: rotate(360deg);
    }
}