.kenkokeiei .m-box-mv {
  background: url("/img/workplace/img_mv_kenkokeiei_pc.jpg") no-repeat center;
  background-size: cover;
}
@media screen and (max-width: 768px) {
  .kenkokeiei .m-box-mv {
    background-image: url("/img/workplace/img_mv_kenkokeiei_sp.jpg");
  }
}