html, body {
    height: 100%
}
body {
    display: grid;
    place-content: center;
}
main {
    display: grid;
    grid-template-columns: repeat(15, 1fr);
    grid-template-rows: repeat(15, 1fr);
    gap: 10px 20px;
}
div {
    height: 10px;
    width: 2px;
    font-size: 8px;
    background: #000;
}