If sometimes you receive unreadable or over sized messages from people using the original yahoo client this little patch could solve the problem. The yahoo format is not always properly rendered but it will be more close to what it should be.
To test it, you have to receive decorated (tweaked font, size or color) messages from yahoo client when using SC. The patch does not affect usual chat from SC to SC. But the code must be updated if someday we provide message formatting or if bugs it tries to workaround are fixed (in yahoo or jYMSG).
During tests, I found in defaultStyles.css :
Is there a specific reason for which italic texts are styled like that ?