body { margin: 0 }

header { padding: 10px; text-align: center; }
header button, header label { margin: 0 10px; }

.grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 5px;
}

.block {
    aspect-ratio: 1;
    border: 1px solid #000;
    background: #fff;
    padding: 10px;
    text-align: left;
}