Increase top margin for long list items

List items inside `#content` use `var(--space-sm)` as their top margin
because `var(--space)` looks too disjointed for single-paragraph items,
especially single-line items.  However, when a list item contains an
element that itself has a `var(--space)` top margin, the list item's top
margin looks mismatched.

This commit adds a style tweak such that all list items in a list with
any multi-paragraph items will use `var(--space)` for their top margin.
(More specifically, when any item contains a paragraph plus another
block level element, such as another paragraph or a code block.)

Unfortunately, this enhancement does not currently work in Firefox
because it relies on the `:has()` selector.  However, it is only a minor
enhancement, and Firefox plans to support `:has()` in the near future.

Author: jonathanhefner

lib/rdoc/generator/template/rails/resources/css/main.css

@@ -382,6 +382,11 @@ html {
   margin-top: var(--space-sm);
 }
 
+/* Increase top margin for list items when any item has more than one paragraph */
+:where(#content :is(ol, ul):has(> li > p:not(:only-child))) * + li {
+  margin-top: var(--space);
+}
+
 :where(#content) code {
   font-style: normal;
 }