:root {
    --rows: 16;
    --columns: 16;
}

h1 {
    text-align: center;
}

button {
    display: block;
    margin: auto auto 20px;
}

#container {
    display: grid;
    margin: auto;
    grid-template-columns: repeat(var(--columns), auto);
    grid-template-rows: repeat(var(--rows), auto);
    border: 1px solid greenyellow;
    height: 20em;
    width: 20em
}