.btn {
    font-size: 22px;
    color: #fff;
    margin: 5px;
    padding: 7px 22px;
    text-decoration: none;
    border-radius: 25px;
}

.btn-subscribe {
    background: #000;
    color: red;
}

.btn .btn-subscribe:hover {
    background: red;
    transition: .5s;
}