@media (max-width: 767px) {
    div.kc-logo-text {
        width: 100%;
        background-image: url(../img/m_hdr.jpg);
        height: 90px;
    }
}

@media (min-width: 768px) {
    div.kc-logo-text {
        background-image: url(../img/header.jpg);
    }
}