Text editors

Found a nice, simple guitar chord generator here.  The code seems to paste into the HTML editor OK but there are a couple of problems.  The line below the top row of circles (denoting the head of the guitar) is missing in Moodle.  Also, sometimes, a second set of circles appears - especially if I have been trying to edit the code.

I am probably doing something extremely stupid but I can't see it.

Thanks

David Berry