SO-42533479

by David Thomas

HTML

<div class="display-block">

  <img src="image">
  <img src="image">
  <img src="image">
  <img src="image">


</div>


<div class="display-block">

  <img src="image">
  <img src="image">
  <img src="image">


</div>

CSS

div.display-block {
  margin-bottom: 1em;
}

img {
  box-shadow: 0 0 3px 1px limegreen;
  height: 4em;
  width: 2em;
  opacity: 0.2;
}

img:first-child,
img:nth-last-child(4) ~ img {
  opacity: 1;
}