It breaks because no fonts are loaded. Google fonts are replaced with Arial. Font Awesome is replaced by notation depending on the browser.
The CDN has an excludes file option. I can include CSS in general, although I thought that kind of was the point of a CDN (as well as images etc). That's why I was looking for a better solution (or what I perceived to be a correct solution).
I can also exlude individual files, although I assume the fonts are the wrong files to exclude, but the CSS files with the references to the fonts. My thinking is that it would be better if there was an absolute reference to fonts, although when I tried that it didn't seem to work.