src/Pure/Thy/html.scala

--- a/src/Pure/Thy/html.scala	Thu Nov 11 13:18:35 2021 +0100
+++ b/src/Pure/Thy/html.scala	Thu Nov 11 13:47:32 2021 +0100
@@ -420,7 +420,8 @@
     base match {
       case None => ""
       case Some(base_dir) =>
-        File.path(dir.absolute.java_path.relativize(base_dir.absolute.java_path).toFile).implode
+        val path = File.path(dir.absolute.java_path.relativize(base_dir.absolute.java_path).toFile)
+        if (path.is_current) "" else path.implode + "/"
     }
 
   def isabelle_css: Path = Path.explode("~~/etc/isabelle.css")