@stulip
I have been trying to add a custom font family to editor html:
I added jf-flat-regular-webfont.woff, jf-flat-regular-webfont.woff2 files parallel to the editor file.

then i added the custom fonts in the html

finally I applied the font in
contentCSSText: font-size: 45px;  min-height: 200px;  height: 100%; font-family:'jf_flatregular'; , // initial valid
};
but the changes did not reflect.