<ul>
  <li><img src="https://s3-us-west-2.amazonaws.com/s.cdpn.io/331810/sq-sample14.jpg" alt="" /></li>
  <li><img src="https://s3-us-west-2.amazonaws.com/s.cdpn.io/331810/sq-sample14.jpg" alt="" /></li>
  <li><img src="https://s3-us-west-2.amazonaws.com/s.cdpn.io/331810/sq-sample14.jpg" alt="" /></li>
  <li><img src="https://s3-us-west-2.amazonaws.com/s.cdpn.io/331810/sq-sample14.jpg" alt="" /></li>
  <li><img src="https://s3-us-west-2.amazonaws.com/s.cdpn.io/331810/sq-sample14.jpg" alt="" /></li>
  <li><img src="https://s3-us-west-2.amazonaws.com/s.cdpn.io/331810/sq-sample14.jpg" alt="" /></li>
</ul>

<ul>
  <li><img src="https://s3-us-west-2.amazonaws.com/s.cdpn.io/331810/sq-sample14.jpg" alt="" /></li>
  <li><img src="https://s3-us-west-2.amazonaws.com/s.cdpn.io/331810/sq-sample14.jpg" alt="" /></li>
  <li><img src="https://s3-us-west-2.amazonaws.com/s.cdpn.io/331810/sq-sample14.jpg" alt="" /></li>
  <li><img src="https://s3-us-west-2.amazonaws.com/s.cdpn.io/331810/sq-sample14.jpg" alt="" /></li>
  <li><img src="https://s3-us-west-2.amazonaws.com/s.cdpn.io/331810/sq-sample14.jpg" alt="" /></li>
  <li><img src="https://s3-us-west-2.amazonaws.com/s.cdpn.io/331810/sq-sample14.jpg" alt="" /></li>
  <li><img src="https://s3-us-west-2.amazonaws.com/s.cdpn.io/331810/sq-sample14.jpg" alt="" /></li>
</ul>

<ul>
  <li><img src="https://s3-us-west-2.amazonaws.com/s.cdpn.io/331810/sq-sample14.jpg" alt="" /></li>
  <li><img src="https://s3-us-west-2.amazonaws.com/s.cdpn.io/331810/sq-sample14.jpg" alt="" /></li>
  <li><img src="https://s3-us-west-2.amazonaws.com/s.cdpn.io/331810/sq-sample14.jpg" alt="" /></li>
  <li><img src="https://s3-us-west-2.amazonaws.com/s.cdpn.io/331810/sq-sample14.jpg" alt="" /></li>
  <li><img src="https://s3-us-west-2.amazonaws.com/s.cdpn.io/331810/sq-sample14.jpg" alt="" /></li>
  <li><img src="https://s3-us-west-2.amazonaws.com/s.cdpn.io/331810/sq-sample14.jpg" alt="" /></li>
  <li><img src="https://s3-us-west-2.amazonaws.com/s.cdpn.io/331810/sq-sample14.jpg" alt="" /></li>
  <li><img src="https://s3-us-west-2.amazonaws.com/s.cdpn.io/331810/sq-sample14.jpg" alt="" /></li>
  <li><img src="https://s3-us-west-2.amazonaws.com/s.cdpn.io/331810/sq-sample14.jpg" alt="" /></li>
</ul>
ul{
  list-style: none outside none;
  margin: 0;
  padding: 0;
  text-align: center;
  
  li {
    width: 50px;
    height: 50px;
    border-radius: 50%;
    display: inline-block;
    margin: 5px;
    opacity: .5;
  }
  li:nth-last-child(3n):first-child ~ li:nth-child(n+3):nth-child(-n+5){
      opacity: 1;
    }
  
  img {
    max-width: 100%;
    border-radius: 50%;
  }
}

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

This Pen doesn't use any external JavaScript resources.