*{
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}
:root{
    --cell-size :200px;
    --mark-size :calc(var(--cell-size)*0.9);
}
.board{
    width: 100vw;
    height: 100vh;
    display: grid;
    justify-content: center;
    align-content: center;
    justify-items: center;
    align-items: center;
    grid-template-columns: repeat(3,auto);
}
.cell{
    width: var(--cell-size);
    height: var(--cell-size);
    border: 1px solid #000;
    display: flex;
    justify-content: center;
    align-items: center;
    position: relative;
    cursor: pointer;
}
.cell.x,
.cell.circle{
    cursor: not-allowed;
}
.cell:nth-child(1),
.cell:nth-child(2),
.cell:nth-child(3){
    border-top: none;
}
.cell:nth-child(7),
.cell:nth-child(8),
.cell:nth-child(9){
    border-bottom: none;
}
.cell:nth-child(3n+1){
    border-left: none;
}
.cell:nth-child(3n+3){
    border-right: none;
}
.cell.x::before,
.cell.x::after,
.cell.circle::before{
    background-color: black;
}
.board.x .cell:not(.x):not(.circle):hover::before,
.board.x .cell:not(.x):not(.circle):hover::after,
.board.circle .cell:not(.x):not(.circle):hover::before,
.board.circle .cell:not(.x):not(.circle):hover::after{
    background-color: lightgrey
}
.cell.x::before,
.cell.x::after,
.board.x .cell:not(.x):not(.circle):hover::before,
.board.x .cell:not(.x):not(.circle):hover::after{
    content: '';
    width: calc(var(--mark-size)*0.15);
    height: var(--mark-size);
    position: absolute;
}
.cell.x::before,
.board.x .cell:not(.x):not(.circle):hover::before{
    transform: rotate(45deg)
}
.cell.x::after,
.board.x .cell:not(.x):not(.circle):hover::after{
    transform: rotate(-45deg)
}
.cell.circle::before,
.cell.circle::after,
.board.circle .cell:not(.x):not(.circle):hover::before,
.board.circle .cell:not(.x):not(.circle):hover::after{
    content: '';
    position: absolute;
    border-radius: 50%;
}
.cell.circle::before,
.board.circle .cell:not(.x):not(.circle):hover::before{
    width: var(--mark-size);
    height: var(--mark-size);
}
.cell.circle::after,
.board.circle .cell:not(.x):not(.circle):hover::after{
    background-color: white;
    width: calc(var(--mark-size)*0.7);
    height: calc(var(--mark-size)*0.7);
}
.winning-message{
    display: none;
    position: fixed;
    top: 0;
    right: 0;
    bottom: 0;
    left: 0;
    justify-content: center;
    align-items: center;
    background-color: rgba(0,0,0,0.8);
    color: white;
    font-size: 5rem;
    flex-direction: column;
}
.winning-message.show{
    display: flex;
}
.winning-message button{
    font-size: 3rem;
    background-color: white;
    border: none;
    padding: 0.5rem 1rem;
    cursor: pointer;
    transition: all 0.4s ease-in-out;
}
.winning-message button:hover{
    background-color: black;
    color: white;
}