Change Font family ePub 3 Android

Hi,

I am developping an app in Android with readium.  I am looking for changing fonts dynamically , but I can't.

For changing theme and interline, I use a javascript script:

     javascript:(function(){ReadiumSDK.reader.setBookStyles(JSON.parse('[{"selector": "body", "declarations": { "backgroundColor": "#ffffffff", "color": ""}}]'))})()

And it works. But I can't set "font-family".

How it should be?