The current implementations of the @import and @media rules are incomplete and partly wrong.

CSSImportRule
The main problem here is the wrong implementation of CSSImportRule.styleSheet. Currently it returns the importing style sheet. The correct behavior would be to return the imported style sheet.

Besides this there are only some minor formatting problems in the returned text.

CSSMediaRule
The main problem here is that the implementation especially of the super classes CSSConditionRule and CSSGroupingRule is not complete. Example: as CSSGroupingRule.cssRules is missing you are not able to access the CSS rules inside the media rule.

I will provide unit tests for these points as a pull request.
Additionally I will have a look if I can provide fixes for some of the points. But especially regarding the main problem of CSSImportRule I am not very optimistic...