body{
    background-image: linear-gradient(to left, purple, black);
}

h2, h3{
    color: lightblue;
}

#box {
    text-align: center;
}

#field table {
    border-collapse: collapse;
    font-size: 150%;
    font-family: san-serif;
    font-weight: bold;
    display: inline-block;
}

#field table td {
    background-color: darkgreen;
    width: 30px;
    min-width: 30px;
    height: 30px;
    min-height: 30px;
    border: 1px solid black;    
}

button {
    width: 100px;
    height: 30px;
    background-color:lightblue;
    color: blue;
    font-weight: bolder;
    border-radius: 20px 20px 20px 20px;
}