*{
    padding: 0;
    margin: 0;
}
:root {
    --grid-cols: 1;
    --grid-rows: 1;
}

#griddiv {
    display: grid;
    grid-template-rows: repeat(var(--grid-rows), auto);
    grid-template-columns: repeat(var(--grid-cols), 1fr);
    width: 500px;
    height: 500px;
    align-items: stretch;
}

.grid-item {
    border: 1px solid #000000;
    text-align: center;
}