ul {
  list-style-type: none;
  margin: 0;
  padding: 0;
  overflow: hidden;
  background-color: #333;
}

li {
  float: left;
  position: relative;
}

ul li.social {
  float: right;
  border-left: 1px solid #555; /* This creates the line you want */
  border-right: none;
}

li a {
  display: block;
  color: white;
  text-align: center;
  padding: 14px 16px;
  text-decoration: none;
}

li a:hover {
  background-color: #111;
}
li:not(:last-child)::after {
  content: "";
  position: absolute;
  right: 0;
  top: 25%;
  height: 50%;
  width: 1px;
  background-color: #555;
}