I think your issue is you are trying to force the font style in the @font, rather than USE a style and or weight in the "class"
The default, unless specified: is normal
if you want Bold: font-weight: bold, if you want italic: font-style: italic;
font-family only sets the family (members)
BTW My Kindle requires the FONT (internal Metrics) be correct for style and weight. Simply substituting a heavy (normal) font for Bold in the @font , 'no work'
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