The end-goal isn't to restrict, but rather safeguard readers (avoid injecting questionable JS that's everywhere on the web). Is styling what you're after? Something else? Happy to consider different scenarios and open those up.
Oh, I see. I completely understand no JS, I just want the freedom to use HTML & CSS to add some dimensionality (eg floats, sidebars) and images (eg captions) to plain text.
"Note: style attributes are currently blocked via Content-Security-Policy."
That's probably not for me. Restrictions on HTML are a stopper.