Logic cannot make sty files. They are proprietary style files for yamaha personal keyboards.
However hope is not completely lost. These are the steps I would take. Keep in mind I am in Logic 7 so the step by step may ot be exact.
If you create a midi file from your project (select your midi regions>File menu>Export>Selection as Midi File) you can then convert this file into sty. Unfortunately the only one I have seen are for windows:
http://www.jososoft.dk/yamaha/softwa...tyle/index.htm
http://biphome.spray.se/smeten/yamaha/dow.htm
last link on this page
If you do some searching on google you might be able to find a MIDI to STY converter for mac.