Lists with more than a few words per item are difficult to read with no extra spacing between the individual points (both for numbered and unnumbered lists). I'm not sure how much spacing would be necessary (perhaps the same as between paragraphs?)

I agree that this looks somewhat suboptimal. However, simply adding the paragraph margin to list points (which is, jftr, a margin-bottom of 0.8em) is not really an option. It would look nice on multi-line points:

However, single-line items look weird:

With 0.5em, the spacing between multi-line items is still noticable:

But single-line points do not look as broken:

Let's see what others have to say.
0.5em looks good to me 馃憤 (better than without spacing and better than paragraph spacing)
Since I added the newcomer tag, here's a hint: app/assets/stylesheets/markdown-content.scss is a good file to start!
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Since I added the newcomer tag, here's a hint:
app/assets/stylesheets/markdown-content.scssis a good file to start!