.parent{position:relative;overflow:hidden;display:inline-flex;height:90vh}.child1{position:absolute;width:100%;height:100%;top:0;left:0}.child2{position:absolute;width:100%;height:100%;top:90vh;left:0}img.child1,img.child2{-o-object-fit:cover;object-fit:cover}.before{background:#eee;transition:transform 1.5s ease-in-out;transform:translateY(-100%);display:flex;justify-content:center;align-items:center}.after{transform:translateY(0)}