body {
    background-image: url("https://bettysgraphics.neocities.org/images/backgrounds/pattern%20559.gif");
    margin: 200px;
    padding: 48px 24px;
    box-sizing: border-box;
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
    gap: 24px;
}
div.gallery img {
  width: 100%;
  height: auto;
  display: block;
}
.responsive {
  flex: 0 1 calc(50% - 12px);
  max-width: calc(50% - 12px);
  box-sizing: border-box;
}