<div class="btn-group">
  <button class="btn">
    Save
  </button>

  <button class="btn">
    Revert
  </button>
</div>

/* .btn-group .btn:first-child {
  background-color: blue;
  color: white;
} */

.btn-group + .btn {
  background-color: blue;
  color: white;
}