Use the text parser to parse CSS

core/modules/parsers/textparser.js

@@ -27,6 +27,7 @@ exports["text/plain"] = TextParser;
 exports["application/vnd.tiddlywiki2"] = TextParser;
 exports["application/javascript"] = TextParser;
 exports["application/json"] = TextParser;
+exports["text/css"] = TextParser;
 
 })();