Rounded grid of images

  <div class="gallery">
    <img src="https://picsum.photos/id/1029/500/500" alt="a big park inside a modern city">
    <img src="https://picsum.photos/id/1047/500/500" alt="a small street between building">
    <img src="https://picsum.photos/id/1067/500/500" alt="seen from the sky of a big city">
    <img src="https://picsum.photos/id/122/500/500" alt="a bridge in the night">
  </div>

.gallery {
  --s: 200px; /* control the size */
  --g: 8px;   /* control the gap */
  
  display: grid;
  grid: auto-flow var(--s)/repeat(2,var(--s));
  gap: var(--g);
}
.gallery > img {
  width: 100%; 
  aspect-ratio: 1;
  cursor: pointer;
  filter: grayscale();
  z-index: 0;
  transition: .25s,z-index 0s .25s;
}
.gallery > img:hover {
  width: calc(200% + var(--g));
  filter: grayscale(0);
  z-index: 1;
  --_c: 50%;
  transition: .4s,z-index 0s;
}
.gallery > img:nth-child(1){
  clip-path: circle(var(--_c,55% at 70% 70%));
  place-self: start;
}
.gallery > img:nth-child(2){
  clip-path: circle(var(--_c,55% at 30% 70%));
  place-self: start end;
}
.gallery > img:nth-child(3){
  clip-path: circle(var(--_c,55% at 70% 30%));
  place-self: end start;
}
.gallery > img:nth-child(4){
  clip-path: circle(var(--_c,55% at 30% 30%));
  place-self: end;
}

body {
  margin: 0;
  min-height: 100vh;
  display: grid;
  place-content: center;
  background: #A8DBA8;
}