Sorry if you feel I misquoted you, it was not intentional. I may be wrong because my KoboGlo is only two days old, but I read on the support forum that any Kobo font you wish to add should include a regular, italic, bold and bolditalic font. This leaves aside stand alone fonts like Linux Libertine Display or smallcaps (semibolds somewhere?).
Nevertheless, I added Linux Libertine to my Kobo and the Linux Libertine Display as well (I named it Linux Libertine Display-Regular ???)
You sent a nice dropcap screenshot. Up to now, I did not manage to display properly the dropcaps for my books (except with the six inch PDF version of my book) with the Kobo Glo. If you find a solution to get a normal display of them, I'll be happy to try it.
There is not need to speak French for this. The CSS file is quite standard, and who cares about the story?
