Help with w3schools slideshow

[matthewk227]

https://www.w3schools.com/howto/tryit.asp?filename=tryhow_js_slideshow

So I basically copied this whole thing but the css and js are externally because my school project requires it to be. When the website loads, it is supposed to display the first image in the slideshow. However, when I loaded it up with everything linked, it is just blank with no image shown. It makes me click one of the dots/one of the arrows to see an image. Can anyone help me fix?

gallery.htmlgallery.cssgallery.js