Edit in JSFiddle

.container{
	height: 100px;
	background: #7396a1;
    color: #fff;
    width: 300px;
    margin-left: auto;
    margin-right: auto;
}
.content {
    text-align: center;
	position: relative;
	top: 50%;
	-webkit-transform: translateY(-50%);
	-o-transform: translateY(-50%);
	transform: translateY(-50%);
}

<div class="container">
    <div class="content">I'm aligned vertically!</div>
</div>