.ad-zone {
  width: 100%;
  max-width: 728px;
  margin: 1rem auto;
  text-align: center;
  overflow: hidden;
}

.ad-zone[hidden] {
  display: none !important;
}

@media (min-width: 768px) {
  .ad-zone {
    width: min(970px, calc(100vw - 2.5rem));
    max-width: 970px;
    min-height: 250px;
    position: relative;
    left: 50%;
    transform: translateX(-50%);
    margin-left: 0;
    margin-right: 0;
  }
}