body, html {
    margin: 0;
    padding: 0;
    height: 100vh;
}

body {
    display: flex;
    justify-content: center;
    align-items: center;
    flex-direction: column;
}

.board {
    aspect-ratio: 1;
    height: 80%;
    border: 3px solid black;
    display: grid;
    grid-template: 1fr 1fr 1fr / 1fr 1fr 1fr;
}

.cell {
    border: 1px solid black;
    display: flex;
    justify-content: center;
    align-items: center;
    font-size: 5rem;
}