The standard CodeMirror approach to setting fonts will not work because of what NM did in the first few lines of scriptcase8.css:
*{
font-family: Arial, Helvetica, sans-serif;
font-size: 12px;
}
Really bad practice using a catch-all like that.
As a workaround, you can edit the theme css file for your new theme and put this at the top of the file:
.CodeMirror-code div pre span span {font-family: Courier New;}
It will give you the font that you want, however using the theme popup to change to another theme will not change the font back until you reload the page (like clicking on another event script).
Dave