CSS isn't loading after DNS switch from *.netlify.app to custom domain

Recently we started using a custom domain (managed externally) on one of our netlify sites, https://opencontainers.netlify.app/. Since switching to https://opencontainers.org/, build previews and the live site can’t seem to find their CSS:

The CSS is loaded in using a relative path, i.e. <style href="css/styles.css">, so it’s not an absolute URL issue. Additionally, when I inspect the source of the page and download the generated files, the CSS file exists on the server at the location specified, so I don’t think that’s the issue either.

Is this a DNS propagation issue? The switch was performed earlier today.

Cheers,
Celeste

hmm, could you do me a favour and turn off asset optimization, and see if that changes things?