body {
    padding: 2rem;
    transition: .5s;
}
.dark-theme {
    background: #000;
    color: #ddd;
}
#btn {
    background: #0bd;
    padding: 1rem;
    margin-bottom: 2rem;
    font-size: 1rem;
    color: #fff;
    border-radius: 8px;
    border: 0;
    cursor: pointer;
}