HTML:

<div class="wrapper">
    <div class="outer">
        <div class="inner">
            centered
        </div>
    </div>
</div>

CSS:

.wrapper {
  height: 600px;
  text-align: center;
}
.outer {
  display: table;
  height: 100%;
  width: 100%;
}
.outer .inner {
  display: table-cell;
  text-align: center;
  vertical-align: middle;
}