It depends what you want to say, but of is more likely.
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Blue Jaydepends what you want to saysay:
Blue Jayfocus on is normally used when describing the whole thingwhen you say 'the whole thing' what do you mean? is it the main topic?
Blue Jayfocus in most often appear in contexts which refer to one or more aspects of the whole'one or more aspects of the whole' - meaning for example main topic- 'animals', within this t