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

body {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    background-color: #333;
}

#game-board {
    --cell-size: 20vmin;
    --cell-gap: 2vmin;

    position: relative;
    display: grid;
    grid-template-columns: repeat(4, var(--cell-size));
    grid-template-rows: repeat(4, var(--cell-size));
    gap: var(--cell-gap);
    border-radius: 1vmin;
}

.cell {
    background-color: #444;
    border-radius: 1vmin;
}

.tile {
    --y: 1;
    --x: 2;
    position: absolute;
    /* top: 0; */
    /* top: calc(1 * (20vmin + 2vmin)); */
    top: calc(var(--y) * (var(--cell-size) + var(--cell-gap)));
    /* left: 0; */
    /* left: calc(2 * (20vmin + 2vmin)); */
    left: calc(var(--x) * (var(--cell-size) + var(--cell-gap)));
    display: flex;
    justify-content: center;
    align-items: center;
    width: 20vmin;
    height: 20vmin;
    border-radius: 1vmin;
    font-family: Arial, Helvetica, sans-serif;
    font-size: 7.5vmin;
    font-weight: bold;
    background-color: hsl(25, 60%, var(--bg-lightness));
    color: hsl(20, 25%, var(--text-lightness));
    transition: 100ms;
    animation: show 200ms;
}

@keyframes show {
    0% {
        opacity: 0.5;
        transform: scale(0);
    }
}