One important thing is to avoid adjusting alignments between two things by offseting against a third one. Typically, offsetting both the icon and text relative to container. And less infernal approach is the align the icon relative to text (eg: use percent (or em!!) vertical align for icon to offset relative to text), and _then_ adjusting centering in container.

Ho, and take car of sub pixel when adjusting, they cumulate, and rounding will bite you !