.btn-dark,
input[type="submit"] {
    border: solid 2px #1f1f1f;
    background: transparent;
    color: #1f1f1f;
}

    .btn-dark:hover,
    input[type="submit"]:hover,
    .btn-dark.active {
        border: solid 2px #1f1f1f;
        background: #1f1f1f;
        color: #fff;
    }