How to change the font size of preview options when using an input method?

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http://askubuntu.com – I'm using IBus for pinyin in 11.10. A previous AskUbuntu poster mentioned that s/he increased font size to 14 point in Preferences. I'm unable to find a setting in Preferences that allows me to do that. The Chinese characters in the preview box are way too small and barely legible now. Just to be clear, this is not about the Chinese text produced in an application program, it is specifically about the size of the five "candidate" Chinese characters that ibus offers me for selection. (HowTos)