.header-banner {
    background-image: url(http://www.jobs.ie/job-talk/wp-content/uploads/contact_centre.jpg);
}
.header-banner-home {
    background-image: url(http://www.jobs.ie/job-talk/wp-content/uploads/call_centre_HOME.jpg);
}

@media (max-width: 31em) {
    .header-banner { background-image: none; }
    .header-banner-home { background-image: none;}
}