body {
    transition: background 3s ease-in-out;
}

.container {
    width: 50%;
    min-width: 300px;
    padding: 20% 25%;
    text-align: center;
    transition: background 3s ease-in-out;
}

button {
    min-width: 25px;
    margin: 10px;
    padding: 5px;
}