style.css

*{
    padding: 0;
    margin: 0;
}

:root{
    --size-cell : 64px;
    --size-grid : 512px;
    --size-border : 16px;
}

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

    height: 100vh;
}

header{
    margin: 15px;
    display: flex;
    flex-direction: row;
    justify-content: space-evenly;
    align-items: center;

    width: var(--size-grid);
}

#timer{
    width: var(--size-cell);
    text-align: right;
}

.stats{
    width: var(--size-cell);
    text-align: right;
}

main{
    width: var(--size-grid);
    height: var(--size-grid);

    border: var(--size-border) solid #999999;

    position: relative;
}

.gameContainer{
    display: flex;
    flex-direction: row;
    flex-wrap: wrap;
    align-content: flex-start;

    width: var(--size-grid);
    height: var(--size-grid);
}

.cell{
    height: var(--size-cell);
    width: var(--size-cell);
}
.cell>img{
    height: var(--size-cell);
    width: var(--size-cell);

    position: absolute;

    image-rendering: crisp-edges;
}
.cell>.hidden:hover{
    visibility: hidden;
}
.hover:hover+.hidden{
    visibility: hidden;
}

#gameover{
    position: absolute;
    top: 0;
    left: 0;

    width: var(--size-grid);
    height: var(--size-grid);
    
    opacity: 0;
    transition: opacity 1s;
    visibility: hidden;
}

#victory{
    position: absolute;
    top: 0;
    left: 0;

    width: var(--size-grid);
    height: var(--size-grid);
    
    opacity: 0;
    transition: opacity 1s;
    visibility: hidden;
}