[Task] Add unit test cases for ThemeCard component

Task Description: Currently, we run unit tests using jest and co-locate the test files with the source files as can be seen here.

However, the test cases are not yet comprehensive enough and work can be done to cover more grounds. Specifically for this issue, we hope to add test cases for the ThemeCard component.

Deliverable(s): New unit test cases that cover the testing of the ThemeCard component.

Additional Context:

• The ThemeCard component can be found here
• An example for SearchBar can be found here which may serve as a good source for reference

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