I just checked my (meagre) achievements for today on https://stackexchange.com/ and got this:
Where as it should look like this:
The site icons are a bit awry.
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So a bad version of a CSS file was cached (to do with the version hash we append) - causing this issue.
We fixed the version hash issue and purged the cache in the CDN, so should work as expected now (may require a hard refresh in the browser to see).