.ad_top {
  margin: calc(1em - 64px) auto 0;
  text-align: center;
  min-height: 280px;
  transition: 0.5s;
}

.ad_top.mobile {
  display: none;
  margin: auto;
  width: 100%;
  min-height: 0;
  text-align: center;
}

.ad_bottom {
  margin: 4em auto 0;
  text-align: center;
  transition: 0.5s;
}

@media handheld, only screen and (max-width: 600px) {
  .ad_top {
    display: none;
  }

  .ad_top.mobile {
    display: block;
  }
}