h1 {
    text-align: center;
}


td {
    border: 3px solid black;
    padding: 5px;
    text-align: center;
    font-size: 30px;
    width: 50px;
    height: 50px;
    line-height: 50px;
}

td:hover {
    background-color: chartreuse;
    color: red;
}