Review the css and theme also like we do for code using code review module
If by the 'Code Review module' you mean the Coder module, it already supports reviewing the code in themes.


  Beginning with the 5.x-2.x version, this module adds a new UI, core
  support, theme support, and a cache for faster display of unchanged
  files. It also supports rule #severity levels of "minor", "normal",
  and "critical."