style.css

*{
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

:root{
    --cell-size: 7rem;
    --symbol-size: calc(var(--cell-size)*0.7);
    --border-color: #120c09;
    --background-color: #443022;
    --symbol-color: #684d25;
    --hover-color: #58524a;
}

.container{
    width: 100vw;
    height: 100vh;
    display: grid;
    grid-template-columns: repeat(3, auto);
    justify-content: center;
    align-content: center; 
    font-family:sans-serif;
    background-image: url(assets/background.jpg);
    background-size: cover; 
    background-position: center;
}

.cell{
    width: var(--cell-size);
    height: var(--cell-size);
    background-color: var(--background-color);
    border: 10px solid transparent;
    box-shadow: 5px 5px 40px 10px var(--border-color) inset;
    display: flex;
    justify-content: center;
    align-items: center;
    cursor: pointer;
}

/* Styles For Corner Cells */
.cell:first-child,
.cell:nth-child(2),
.cell:nth-child(3){
    border-top: 20px solid var(--border-color);
}

.cell:nth-child(3n + 1){
    border-left: 20px solid var(--border-color);
    width: 8rem;
}

.cell:nth-child(3n + 3){
    border-right: 20px solid var(--border-color);
    width: 8rem;
}

.cell:nth-child(7),
.cell:nth-child(8),
.cell:last-child {
    border-bottom: 20px solid var(--border-color);
}


/* Cross Symbol Formation */
.cell.cross::before,
.cell.cross::after,
.container.cross .cell:not(.cross):not(.circle):hover::before,
.container.cross .cell:not(.cross):not(.circle):hover::after  {
    content: '';
    width: calc(var(--symbol-size) * 0.2);
    height: var(--symbol-size);
    background-color: var(--symbol-color);
    position: absolute;
}

.cell.cross::before,
.container.cross .cell:not(.cross):not(.circle):hover::before {
    transform: rotate(45deg);
}

.cell.cross::after,
.container.cross .cell:not(.cross):not(.circle):hover::after {
    transform: rotate(-45deg);
}

.container.cross .cell:not(.cross):not(.circle):hover::before,
.container.cross .cell:not(.cross):not(.circle):hover::after{
    background-color: var(--hover-color);
}

/* Circle Symbol Formation */
.cell.circle::before,
.cell.circle::after,
.container.circle .cell:not(.cross):not(.circle):hover::before,
.container.circle .cell:not(.cross):not(.circle):hover::after {
    content: '';
    border-radius: 50%;
    position: absolute;
}

.cell.circle::before,
.container.circle .cell:not(.cross):not(.circle):hover::before {
    width: var(--symbol-size);
    height: var(--symbol-size);
    background-color: var(--symbol-color);
}

.cell.circle::after,
.container.circle .cell:not(.cross):not(.circle):hover::after {
    width: calc(var(--symbol-size) * 0.6);
    height: calc(var(--symbol-size) * 0.6);
    background-color: var(--background-color);
    box-shadow: 5px 5px 20px 5px var(--border-color) inset;
}

.container.circle .cell:not(.cross):not(.circle):hover::before{
    background-color: var(--hover-color);
}

.cell.cross, .cell.circle{
    cursor: not-allowed;
}

/* Winnig Message */
.message{
    position: fixed;
    left: 0;
    top: 0;
    right: 0;
    bottom: 0;
    background-color: rgba(0, 0, 0, 0.6);
    display: flex;
    justify-content: center;
    align-items: center;
    flex-direction: column;
    gap: 10px;
}

.hidden {
    display: none;
}

.message-text{
    font-size: 5rem;
    color: white;
}

.message button{
    font-size: 3rem;
    padding:  0.5rem 1rem; 
    border: 2px solid black;
    cursor: pointer;
}

.message button:hover {
    color: white;
    background-color: black;
    border: 2px solid white;
}



/* Media Queries */

@media screen and (max-width: 450px) {
    :root {
        --cell-size: 6rem;
    }

    .cell{
        border: 8px solid transparent;
    }

    .cell:nth-child(3n + 1) {
        width: 7rem;
    }

    .cell:nth-child(3n + 3) {
        width: 7rem;
    }
}