I don’t understand how to add my extension locally correctly

I want to use the Draw Tool Extension. In my Autodesk Forge Viewer. When I download the extension like this, it works. https://github.getafreenode.com/autodesk-platform-services/aps-extensions/blob/main/public/extensions/DrawToolExtension

<link rel="stylesheet" href="http://cdn.jsdelivr.net/gh/autodesk-forge/forge-extensions/public/extensions/DrawToolExtension/contents/main.css"> 
<script src="http://cdn.jsdelivr.net/gh/autodesk-forge/forge-extensions/public/extensions/DrawToolExtension/contents/main.js"></script> 

But I would like to change the extension code for my needs. I specify it locally

<script type="text/javascript" src="main.js"></script>
<link rel="stylesheet" href="main.css">

But it stops working, and I don’t understand why