Bootstrap 4

HTML

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-alpha.2/css/bootstrap.min.css">
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-alpha.2/js/bootstrap.min.js"></script>
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootswatch/3.3.7/flatly/bootstrap.min.css">
<div class="row" style="height:200px;background-color:grey">
   <div class="col-md-10">
      <div class="this-div">
      <span>How to center this vertically/horizontally</span>
      </div>
   </div>
   <div class="col-md-2">
      <div class="that-div">
      <span>This too</span>
      </div>
   </div>
</div>

CSS

.col-md-10{
  height: 200px;
}
.col-md-2{
  height: 200px;
}

.this-div {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
}

.that-div {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
}