<div class="gallery">
  <img src="https://picsum.photos/id/1040/300/300" alt="a house on a mountain">
  <img src="https://picsum.photos/id/106/300/300" alt="sime pink flowers">
  <img src="https://picsum.photos/id/136/300/300" alt="big rocks with some trees">
  <img src="https://picsum.photos/id/110/300/300" alt="a cool landscape">
</div>

.gallery {
  --s: 150px; /* control the size */
  display: grid;
  grid: auto-flow var(--s) / repeat(2,var(--s));
  gap: 10px;
  place-items: center;
  margin: calc(var(--s)/2);
  transform: rotate(45deg);
}
.gallery > img {
  width: 100%; 
  aspect-ratio: 1;
  object-fit: cover;
  transform: rotate(-45deg);
}


body {
  margin: 0;
  min-height: 100vh;
  display: grid;
  place-content: center;
  background: #aabbfb;
}