[8140david]

This makes sense, thanks.

I was toying with the idea but didn't want to trim 3 fonts (regular, bold, italic) on the website I was mentioning, as this is a rather slow operation. But doing it with Calibre is easy and very quick, so I've done it.

And it works!
I personnally prefer to use the Georgia font on my Kobo Aura.
But it's also fine with the document default, in this case, Stix.

So here are the current declarations concerning Stix in the css of the epub (I didn't need bold italic):

@font-face
    {
    font-family: 'Stix';
    font-weight: normal;
    font-style: normal;
    src: url('../Fonts/STIX-Regular.otf');
    }
@font-face
    {
    font-family: 'Stix';
    font-weight: normal;
    font-style: italic;
    src: url('../Fonts/STIX-Italic.otf');
    }
@font-face
    {
    font-family: 'Stix';
    font-weight: bold;
    font-style: normal;
    src: url('../Fonts/STIX-Bold.otf');
    }
body
    {
    font-family: 'Stix'
    }
.maths
    {
    font-family: 'Stix';
    }