Font typeface options are "generic": sans, serif, mono.
They're encoded like this:
public static final String HTML_FONT_FAMILY_SANS = "font-family: Arial, Myriad, 'Liberation Sans', sans-serif;";
public static final String HTML_FONT_FAMILY_SERIF = "font-family: 'Times New Roman', Times, 'Liberation Serif', serif;";
public static final String HTML_FONT_FAMILY_MONO = "font-family: 'Courier New', Courier, 'Liberation Mono', monospace;";
with specific font mappings for Windows, Mac and Linux.
I could make the change to Calibri, but then someone would complain about "where did Arial go"?