Why does the webpage work on my PC but not on Github? [closed]

I have a page, you can see it on github. The strange thing is that the page works fine locally on my computer but it does not work online after I uploaded on to github.

This is the page
https://vyha18.github.io/video/van2.html#

All css, javascript and html are in the van2.html#, you can see the source code by viewing source or you can click here “view-source:https://vyha18.github.io/video/van2.html#”

You can copy all the source code to a html file on your PC and try to test it.

Make sure you change 'van.mp3' to 'https://vyha18.github.io/video/van.mp3' on your own html file.

Note: To test the page, click on “Tong Hop Van“, then click OK. If you can hear some sound, then it works.

Note: I saved the html file using UTF-8 before uploading it to github.

What is causing the problem?