CSS Flex | Vertical & horizontal center

for post http://stackoverflow.com/questions/34217260/css-easiest-way-to-centering-elements-both-horizontally-and-vertically-using-f

HTML

<div class="container">
  <div class="item"></div>
  <div class="item"></div>
</div>

CSS

.container {
  width: 100%;
  height: 500px;
  background: #ccc;
  display: flex;
  justify-content: center;
  align-items: center;
}

.item {
  width: 100px;
  height: 100px;
  background: tomato;
  border: 1px solid #fff;
}