.box {
}

body {
    overflow: hidden;
}

.grow {
  animation-duration: 0.7s;
  animation-name: changeHeight;
  animation-fill-mode: forwards;
}

@keyframes changeHeight {
  100% {
    transform: translateY(-120%);
  }
}

#img1 {display:block;}
#img2 {display:none}

@media all and (max-width: 1000px) {
    #img1 {display: none;}
    #img2 {display: block;}
}