*::after,*::before{
    box-sizing: border-box;
}
/* he ::after selector inserts something after the content of each selected element(s). ::before selector to insert something before the content.*/

:root{
    --cell-size: 100px;
    --mark-size: calc(var(--cell-size) * .9);
}

body{
    margin: 0;
}
.board{
    width: 100vw;
    height: 100vh;
    display: grid;
    justify-content: center;
    align-content: center;
    grid-template-columns: repeat(3,auto); 
    /* will create 3 seprate coloumns of auto size */
    justify-items: center;
    align-items: center;
}
.cell{
    width: var(--cell-size);
    height: var(--cell-size);
    border: 1px solid black;
    display: flex;
    justify-content: center;
    align-items: center;
    position: relative;
    cursor: pointer;
}
.cell.x, .cell.circle{
    cursor: not-allowed;
}
.cell:first-child,.cell:nth-child(2),.cell:nth-child(3){
    border-top: none;
}
.cell:nth-child(3n+1){
    border-left: none;
}
.cell:nth-child(3n+3){
    border-right: none;
}
.cell:last-child,.cell:nth-child(8),.cell:nth-child(7){
    border-bottom: none;
}
.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{
    background-color: lightgray;
}
.cell.x::before,
.cell.x::after,
.cell.circle::before{
    background-color: black;
}

.cell.circle::after{
    background-color: black;
}
.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) * .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{
    width: calc(var(--mark-size) * .7);
    height: calc(var(--mark-size) * .7);
    background-color: white;
}

.winning-message{
  display: none;
  position: fixed;  
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background-color: rgba(0, 0, 0, .9);
  justify-content: center;
  align-items: center;
  color: white;
  font-size: 5rem;
  flex-direction: column;
}
.winning-message button{
    font-size: 3rem;
    background-color: white;
    border: 1px solid black;
    padding: .25em .5em;
    cursor: pointer;
}
.winning-message button:hover{
    background-color: black;
    border-color: white;
    color: white;
}
.winning-message.show{
    display: flex;
}