div {
  box-sizing: border-box;
}
.banner-space-wrapper {
  width: 100%;
  display: flex;
  --gap: 30px;
  gap: var(--gap);
  flex-wrap: wrap;
}
@media (min-width: 640px) {
  .banner-space-wrapper {
    flex-wrap: nowrap;
    flex-direction: column;
  }
}
.banner-space-wrapper .banner-place {
  aspect-ratio: 240 / 400;
  background-color: blue;
  width: calc(50% - var(--gap)/2);
}
@media (min-width: 640px) {
  .banner-space-wrapper .banner-place {
    width: 240px;
  }
}