What is the best way of centering the most effective?

    
the <div>
</div>


and its css:

.container {
 position: absoulute;
 width: 100%;
 height: 100%;
}
.container-inner {
 width: 400px;
 height: 400px;
}



I need to do to div with class container-inner lined at the center of the browser horizontally and vertically.


What is by far the most simple, light in weight and the size of the code and cross-browser solution?