// * Vartical & Horizontal Centering (IE8 and above. use position.)
@mixin vh-center($axis:xy) {
    position: relative;
    & > * {
        position: absolute;
        @if $axis == x {
            left: 0;
            right: 0;
            margin-left: auto;
            margin-right: auto;
        } @elseif $axis == y {
            top: 0;
            bottom: 0;
            margin-top: auto;
            margin-bottom: auto;
        } @else {
            top: 0;
            left: 0;
            right: 0;
            bottom: 0;
            margin: auto;
        }
    }
}