.btn-posting {
    /* Add your styles here */
}

@media (min-width: 992px) { /* lg */
    .btn-posting {
        width: 25%;
    }
}

@media (min-width: 768px) and (max-width: 991px) { /* md */
    .btn-posting {
        width: 25%;
    }
}

@media (max-width: 767px) { /* sm */
    .btn-posting {
        width: 100%;
    }
}