koshotayl

width: 100%;
 height: 100%;
 object-fit: cover; или object-fit: contain;

let res = [...document.querySelectorAll('.block')].map(i => i.children.length);
console.log(res);

const blocks = document.getElementsByClassName('block');
const stats = [];
for(block of blocks) {
  const size = block.getElementsByClassName('item').length;
  stats.push(size);
}
alert(stats);