Sass mixin for Compass that vertically centres a descendant of the element in which it is included. The mixin neatly wraps-up Sebastian Ekström's updated solution in http://zerosixthree.se/vertical-align-anything-with-just-3-lines-of-css/

_mixins.scss

@import "compass/css3/transform";

@mixin vertically-centre-descendant($descendant-selector, $descendant-position: relative) {
    @include transform-style(preserve-3d);
    position: relative;

    #{$descendant-selector} {
        @include transform(translateY(-50%));
        position: $descendant-position;
        top: 50%;
        @content
    }
}