<div>
  <img src='https://images.unsplash.com/photo-1513360371669-4adf3dd7dff8?crop=entropy&cs=tinysrgb&fit=max&fm=jpg&ixid=M3wzMjM4NDZ8MHwxfHJhbmRvbXx8fHx8fHx8fDE2OTM4OTg5MzR8&ixlib=rb-4.0.3&q=80&w=400' alt=''>
  <img src='https://images.unsplash.com/photo-1487300001871-12053913095d?crop=entropy&cs=tinysrgb&fit=max&fm=jpg&ixid=M3wzMjM4NDZ8MHwxfHJhbmRvbXx8fHx8fHx8fDE2OTM4OTg5MzR8&ixlib=rb-4.0.3&q=80&w=400' alt=''>
  <img src='https://images.unsplash.com/photo-1533743983669-94fa5c4338ec?crop=entropy&cs=tinysrgb&fit=max&fm=jpg&ixid=M3wzMjM4NDZ8MHwxfHJhbmRvbXx8fHx8fHx8fDE2OTM4OTg5MzR8&ixlib=rb-4.0.3&q=80&w=400' alt=''>
  <img src='https://images.unsplash.com/photo-1530991671072-ac4f81c2c3c1?crop=entropy&cs=tinysrgb&fit=max&fm=jpg&ixid=M3wzMjM4NDZ8MHwxfHJhbmRvbXx8fHx8fHx8fDE2OTM4OTg5ODN8&ixlib=rb-4.0.3&q=80&w=400' alt=''>
  <img src='https://images.unsplash.com/photo-1472491235688-bdc81a63246e?crop=entropy&cs=tinysrgb&fit=max&fm=jpg&ixid=M3wzMjM4NDZ8MHwxfHJhbmRvbXx8fHx8fHx8fDE2OTM4OTkwMTV8&ixlib=rb-4.0.3&q=80&w=400' alt=''>
  <img src='https://images.unsplash.com/photo-1585373683920-671438c82bfa?crop=entropy&cs=tinysrgb&fit=max&fm=jpg&ixid=M3wzMjM4NDZ8MHwxfHJhbmRvbXx8fHx8fHx8fDE2OTM4OTkwNjh8&ixlib=rb-4.0.3&q=80&w=400' alt=''>
</div>

img:not(:hover) {
  filter: blur(4px);
}
/*
↓ これと同じ意味 ↓

img {
  filter: blur(4px);
}
img:hover {
  filter: none;
}
*/

div {
  display: grid;
  gap: 1rem;
  grid-template-columns: repeat(3, 1fr);
}
img {
  width: 100%;
  aspect-ratio: 3/2;
  object-fit: cover;
}