> Please serve your javascript directly, even if it is a third party library.
CodePen is a frontend playground. You cannot host anything there, so third-party scripts are a requirement.
You can either disable the third-party block or just don't play with it.
Yeah the JSON file with key mappings (http://s.cdpn.io/190177/keyboard_.json) appears to have an incorrect mapping for ';'.
It says 186, but console.log(code) returns 59 for me. If I update the javascript to replace the 186 with 59 the sound will play, but to get proper CSS effects I think the JSON file needs to be corrected.
Additionally, the "Over" button (;) does not work for me for whatever reason. Firefox 30.