.gallery {
  column-count: 2;       /* TWO columns */
  column-gap: 10px;      /* spacing between columns */
  width: 100%;
  max-width: 1200px;     /* optional central width */
  margin: 0 auto;
}

.gallery img {
  width: 100%;           /* fill column width */
  height: auto;          /* preserve original ratio */
  display: block;
  margin-bottom: 10px; /* spacing between images vertically */
}

body {
  background-color:  #white; /* light gray example */
}