For basic HTML sites Netlify attempts to serve only /index.html in case you try to load your site without a path, for example:
https://your_sub_domain.netlify.app
Or https://your_domain.com
Therefore instead of your project root to be
mainpack
the folder structure of your project root should be
css img js modal svg index.html
Once you make the changes, redeploy again to see if the site displays. Let me know if it works.
I took a look at your html in your repo and it seems some of the images are supposed to be in a svg folder.
Also the js and modal folders is also missing.
Just to show you one example in the copyright section