Refs #4127 images in CSS with url('path or url("path or url(path shou…

…ld be replaced

core/Theme.php

@@ -59,7 +59,7 @@ public function rewriteAssetsPathToTheme($output)
             '~(src|href)=[\'"]([^\'"]+)[\'"]~',
 
             // rewrite images in CSS files, i.e. url(plugins/Morpheus/overrides/themes/default/images/help.png);
-            '~(url\()([^\)]?[themes|plugins]+[^\)]+[.jpg|png|gif]?)[\)]~',
+            '~(url\()[\'"]([^\)]?[themes|plugins]+[^\)]+[.jpg|png|gif]?)[\'"][\)]~',
 
             // rewrites images in JS files
             '~(=)[\s]?[\'"]([^\'"]+[.jpg|.png|.gif]?)[\'"]~',