<div class="container">
  <div class="element">
    This is content
  </div>
</div>

.container { 
  height: 400px;
  position: relative;
  border: 3px solid green; 
}

.container .element {
  margin: 0;
  position: absolute;
  top: 50%;
  left: 50%;
  width: 150px;
  height: 150px;
  background-color: red;
  -ms-transform: translate(-50%, -50%);
  transform: translate(-50%, -50%);
}