private static Set<String> getCssClassNames(String fileName, String cssSource,
Set<JClassType> imports, TreeLogger logger) throws UnableToCompleteException {
SourceCode sourceCode = new SourceCode(fileName, cssSource);
CssTree tree;
try {
tree = new GssParser(sourceCode).parse();
} catch (GssParserException e) {
logger.log(TreeLogger.ERROR, "Unable to parse CSS", e);
throw new UnableToCompleteException();
}
return new ClassNamesCollector().getClassNames(tree, imports);