style.css

.nav {
  text-align: center;
}

.nav > li {
  float: none;
  display: inline-block;
}

.icon {
  width: 60px;
  height: 60px;
}

.online {
  background-color: lightgreen;
}

.offline {
  background-color: lightpink;
}

.missing {
  background-color: yellow;
}