.internalAndKidneyHero {
    background-image: url(../img/bg-internal-and-kidney.jpg);
    background-position: center;
}

@media screen and (max-width: 599px) {
    /* 599pxまでの幅の場合に適応される */
    .internalAndKidneyHero {
        background-position-x: 38%;
    }
}