Some time ago, I had issues when enabling CSS optimisation using the Deco theme (which is also used by this site as well). I've solved the issue quite some time ago, but never got around to actually presenting the solution.

While trying to speed-up the site by turning on caching and some optimisations, I've ran into a problem with the Deco theme used on the site. Apparently, when CSS optimisation is turned on, it all gets messed-up (most notably the fonts don't look right).