.fb_box{
    width: 670px;
    background: #fff;
    text-align: center;
}

.contact_big_bnr {
   margin: 20px 0;
}
.contact_big_bnr_sp {
 display: none;
}

@media (max-width: 768px) {
.fb_box {
    width: 90%;
    overflow: hidden;
    margin: 0 auto 20px;
}
  .contact_big_bnr_sp {
    display: inline-block;
    overflow: hidden;
}
    .contact_big_bnr_sp img {
    display: block;
    width: 90%;
    margin: 0 auto 20px;
}
  .contact_big_bnr {
    display: none;
    margin: 0 auto 20px;
}
}