Workspace not working correctly.
I'm following this step by step and it is not working correctly in the video index.html is not showing up in the correct order or correct folder in the workspace.
I'd have to see your code and your workspace folder tree to really know what is going on.
The css folder should contain the style.css file and the js folder should contain the files preview.js, script.js and app.js (if you made an app.js file).
If that's the case and you typed your code just as Guil did, you should be OK.
I did create an app.js file, so my HTML code looks like this:
My script.js code:
alert("Hey, you're back for more?");
My app.js code:
alert("Another message from inside index.html");
I hope that helps.
Stay safe and happy coding!