@media screen and (min-width: 769px), print {
  .add_banner {
    display: block;
    width: 1100px;
    margin: 50px auto 0;
    text-align: center;
  }
  .add_banner a:hover {
    opacity: 0.8;
  }
}

@media screen and (max-width: 768px) {
  .add_banner {
    display: block;
    margin: 20px auto 0;
  }
  .add_banner a {
    display: block;
  }
  .add_banner a img {
    width: 100%;
  }
}