body {
    background: black;
    text-align: center;
    color: white;
    font-family: 'Courier New', monospace;
}
.result {
    margin: 5px auto;
    padding: 5px;
    border: 2px solid white;
    color: white;
    font-size: 20px;
    width: 255px;
    text-align: right;
}

button {
    background: black;
    margin: 5px auto;
    padding: 5px;
    border: 2px solid white;
    color: white;
    font-size: 20px;
    width: 60px;
    font-family: 'Courier New', monospace;
}
button:hover {
    background: #353535;
}
button:active {
    background: gray;
}