#page_in { max-width: 1200px; min-height: 1200px; margin: 0 auto; background: url(../img/kv_pc_touji.jpg) 50% 0 fixed no-repeat; background-size: contain; }

#page_in > section { width: 100%; max-width: 600px; margin: 0 0 0 auto; background: #E8E9F3 url(../img/bg_stripe.png); padding: 50px; box-sizing: border-box; text-align: center; }
@media screen and (max-width: 1200px) {
    #page_in > section { margin: 0 auto; }
  }