The accepted answer works, but if:
use this:
.centered {
position: fixed; /* or absolute */
top: 50%;
left: 50%;
/* bring your own prefixes */
transform: translate(-50%, -50%);
}
More information about centering content in this excellent CSS-Tricks article.
.center{
height: 100vh;
display: flex;
justify-content: center;
align-items: center;
}
Another great guide about flexboxs from CSS Tricks; http://css-tricks.com/snippets/css/a-guide-to-flexbox/