This repo is deployed simultaneously to GitHub Pages and Netlify.

It displays correctly on Netlify. See https://6489cd17207ee90009819190--aip1.netlify.app/.

But deployments to GitHub Pages using actions (currently in beta) doesn't display correctly.

I have viewed the action logs and skimmed through the source code for actions/upload-pages-artifact, upload-artifact, and @actions/artifact. All seems well. I'm yet to look into actions/deploy-pages and the outputted URLs in the action logs.

Screenshots

  Elements tab in dev tools

  Network tab in dev tools

Response headers

The response headers differ from other deployed pages projects. Here, I am comparing my main CSS file with base.css from "square.github.io". Note that this can be a CSS file from any proper working deployed project.

-	plbstl.github.io/icon-previewer	square.github.io
access-control-allow-origin	❌	*
age	872 (higher than others)	4 (sometimes as low as zero)
cache-control	❌	max-age=600
content-security-policy	default-src 'none'; style-src 'unsafe-inline'; img-src data:; connect-src 'self'	❌
content-type	text/html; charset=utf-8 (requested a CSS file!)	text/css; charset=utf-8
expires	❌	approximately 10 mins after Date header
last-modified	❌	Datetime

Conclusion

The assets are obviously not there, that's why GitHub sends a generic 404 HTML. Maybe they're in another location, who knows. I am not done debugging but that's taking some time. I'll switch to classic GitHub Pages on the main branch with a /docs folder. This is very okay for my current setup.

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Edit: I really needed that sleep 🤦‍♂️

The problem is the link tag href attribute. It starts with an absolute path of / instead of /icon-previewer/.

As per http://username.github.io/repository.

See: https://pages.github.com