Div overlay

divOverlay.css

.overlay-container {
    position: relative;
}

.overlay-sibling-under,
.overlay-sibling-upper {
    height: 500px;
    width: 100%;
    position: absolute;
    top: 0;
    left: 0;
}

.overlay-sibling-upper {
    z-index: 10;
    padding-top:50%;
}

divOverlay.html

<!-- Source : http://jsfiddle.net/8wp4xk5g/1/ -->

<div id="overlay-container">
  <div id="map" class="overlay-sibling-under"></div>
  <div id="divSpinner" class="spinner overlay-sibling-upper">
    <i class="fa fa-spinner fa-pulse fa-3x fa-fw" style="color:#FFFFFF;"></i>
    <p>loading</p>
  </div>
</div>