.hero-bg {
    background: 
        linear-gradient(rgba(0, 0, 0, 0.5), rgba(0, 0, 0, 0.5)),
        url('../images/hero-bg-desktop.jpg') center/cover no-repeat;
        min-height: 80vh;
}

@media (max-width: 768px) {
    .hero-bg {
    background: 
        linear-gradient(rgba(0, 0, 0, 0.5), rgba(0, 0, 0, 0.5)),
        url('../images/hero-bg-mobile.jpg') center/cover no-repeat;
}
}