src/Pure/Thy/html.scala

       fonts_css(make_url) + "\n\n" + File.read(isabelle_css))
   }
 
   def init_dir(dir: Path)
   {
-    Isabelle_System.mkdirs(dir)
+    Isabelle_System.make_directory(dir)
     write_isabelle_css(dir)
   }
 
   def write_document(dir: Path, name: String, head: XML.Body, body: XML.Body,
     css: String = isabelle_css.file_name,