Pure CSS solution for centering content always on middle center of parent relative block.

central.css

/*
Pure CSS solution for centering content always on middle center of parent relative block.
*/

.central {
    position: absolute;
    left: 0;
    top: 0;
    width: 100%;
    height: 100%;
    display: table;
}

.central > div {
    display: table-cell;
    vertical-align: middle;
    text-align: center;
}

.central > div > div {
    display: inline-block;
}

markup.html

<div style="position: relative; height: 100%;"> <!-- Any position:relative block or body -->
  <div class="central">
    <div>
      <div>
        Here goes centered content!
      </div>
    </div>
  </div>
</div>