/*#imageContainer {
	position:relative;
	margin:auto;
	width:600px;
	height:450px;
	border:1px solid #cccccc;
}

#imageContainer img {
	display:none;
	position:absolute;
	top:0; left:0;
}
*/
#imageContainer {
  position: relative;
  width: 100%;
  max-width: 600px;
  aspect-ratio: 4 / 3;   /* match your photos (600x450) */
  margin: auto;
  border: 1px solid #ccc;
}
#imageContainer img,
#imageContainer img.rounded-corners {
  display: none;
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  max-width: none;
  object-fit: cover;     /* or contain, if you don't want cropping */
}