diff --git a/ui/src/vendor/css.js/css.js b/ui/src/vendor/css.js/css.js
index 254e6b5e0e..d8ee7160ba 100644
--- a/ui/src/vendor/css.js/css.js
+++ b/ui/src/vendor/css.js/css.js
@@ -148,7 +148,7 @@ fi.prototype.parseRules = function (rules) {
     var ret = [];
 
     // Split all rules but keep semicolon for base64 url data
-    rules = rules.split(/;(?!base64)/);
+    rules = rules.split(/;(?![^\(]*\))/);
 
     //proccess rules line by line
     for (var i = 0; i < rules.length; i++) {