Add attributes to details blocks

[PoignardAzur]

<detail> blocks in the minima theme have no attributes applied; which means they're not aligned with other paragraphs.

This commit adds properties to detail matching those of other block types in minima.

Note that I haven't actually tested this. It worked when I edited the style in the browser, so it should work when compiled from scss, but, yknow, check before merging.

[PoignardAzur]

(Quick ping to remind @raphlinus this PR exists)