Improve verse style (AsciiDoc)
### Problem to solve
In AsciiDoc, a verse is a literary excerpt:
```adoc
content before.
[verse,attribution,citetitle]
____
verse - a literary excerpt, often a poem; attribution with title of source are optional
____
content after.
```
Here's the generated HTML:
```html
<div>
<p>content before.</p>
</div>
<div>
<pre>verse - a literary excerpt, often a poem; attribution with title of source are optional</pre>
<div>— attribution<br>citetitle</div>
</div>
<div>
<p>content after.</p>
</div>
```
And here's how it's rendered on GitLab:

As you can see a margin is added after the `<pre>` element and as a result it's hard to parse for a reader.
Also the `<pre>` element has a "code" style (monospaced font, with a light grey background) but the `<pre>` element represents preformatted text (not necessarily code text): https://developer.mozilla.org/en-US/docs/Web/HTML/Element/pre
As mention above, verse is a literary excerpt, so we should use a sans-serif font.
### Proposal
I think that we should generate the following HTML:
```html
<blockquote class="verse">
<pre class="verse">verse - a literary excerpt, often a poem; attribution with title of source are optional</pre>
<footer>— attribution <cite>citetitle</cite></footer>
</blockquote>
```
And we should also update the stylesheet:

### Links / references
issue