.hero-img {
    position: fixed;
    top: 0;
    left: 0;
    bottom: 0;
    right: 0;
}

.hero-img > img {
    position: absolute;
    top: 50%;
    left: 50%;
    max-height: 90%;
    max-width: 90%;
    transform: translate(-50%, -50%);
}