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Using a style element should have worked too. The HN CSP policy has unsafe-inline which covers both of these things.

Perhaps your problem wasn't with CSP at all, but something else. Maybe a CSS specificity issue?

[edit] - Yeah, I just created this bookmarklet and it worked fine:

javascript:(function(){s=document.createElement('style');s.textContent='*{font-size:20px}';document.head.appendChild(s)})()

Even better!

My solution was a link element with a data: URI. Yours is much more elegant. And works!

Thank you very much!

That would be the problem. The HN policy for styles is:

style-src 'self' 'unsafe-inline'

This means they can include CSS from the same origin, or inline. It would need "data:" adding to the list to allow data URI's as an accepted source.