table,
td {
    text-align: center;
    border: 1px solid black;
    border-collapse: collapse;
    border-color: pink;
}

td:nth-child(3n+4) {
    border-left-width: 4px;
}

tr:nth-child(3n+4)>td {
    border-top-width: 4px;
}

h1 {
    font-size: 65px;
    text-align: center;
}

div {
    display: flex;
    justify-content: center;
}

td {
    font-size: 30px;
    padding: 5px;
}