Prettier blockquotes

[rdeago]

This PR makes blockquotes look like blockquotes, as opposed to mere pieces of italicized text.

This is how a blockquote will look like after merging this PR:

For reference, this is the Markdown source for the blockquote in the image above:

 > Nullam in ipsum eros. Aenean porta mi vitae justo hendrerit, eget pharetra erat tempus.
>
> _— Loremus de Ipsumis, "Dolor sit? Amet!", ch. 19_

[rdeago]

I just converted this PR to draft because I'm incorporating it, together with other improvements, in #23. I will probably close this one once the other one is ready.

[rdeago]

Closing this as the same changes are in #23.

[atiq-cs]

Keeping this separate from updating front end dep library changes is a good idea.