Originally Posted by Valloric
That could then be a bug. I'll take a look at it.
Found it. The book you posted uses @import CSS rules to import external stylesheets. That doesn't currently work in Sigil. This will have to wait until v0.2.0 (I'm starting to sound like a broken record...).
An easy workaround is to just copy the CSS directly and not use the @import rule.
Yes, I know this sucks.
EDIT: Do create an issue for this on the tracker so I remember to get to it when 0.2.0 hits.