I finished writing up and testing some CSS pseudolink styling for toggles. If you want your collapse/expand toggles to appear like normal (Vector skin) links, put the following CSS in your MediaWiki:Common.css:
<pre>
/* For mw-collapsible toggles to make them look like regular links */
/* :visited, :hover, and :active pseudoclasses must always be in that order! */
.pseudolink { cursor:pointer; color:#0645AD; }
.pseudolink:visited { color:#0B0080; }
.pseudolink:hover { text-decoration:underline; }
.pseudolink:active { color:#faa700; }
</pre>
I think that should be built in, to supplement the jQuery MakeCollapsible features in 1.18.
See also, about cursors:
https://bugzilla.wikimedia.org/show_bug.cgi?id=30327
I think the regular pointer cursor is better, and more familiar. The up-down arrows are used for moving window panes.
Version: 1.18.x
Severity: enhancement