Usage patterns
〈事〉をテーマにするto make something the theme (of a work, event, etc.)
This event is themed around environmental issues.
テーマを決めるto decide on a theme
Let's first decide on the theme of the thesis.
テーマに沿うto stick to / follow the theme
Please make sure the presentation content follows the theme.
テーマは〈事〉だthe theme is ...
The theme of this exhibition is 'the future.'