Infra: Increase spacing between complex list items (#3662)

pep_sphinx_extensions/pep_theme/static/style.css

@@ -74,6 +74,15 @@ section#pep-page-section {
     padding: 0.25rem;
 }
 
+/* This is likely very close to the browser default, but we make it a variable
+ * so it can be used in other rules. */
+:root {
+    --paragraph-margin-vertical: 1em;
+}
+p {
+    margin: var(--paragraph-margin-vertical) 0;
+}
+
 /* Header rules */
 h1 {
     font-size: 2rem;
@@ -197,6 +206,18 @@ ol.upperalpha {list-style: upper-alpha}
 ol.lowerroman {list-style: lower-roman}
 ol.upperroman {list-style: upper-roman}
 
+/* We can't express this as a single rule using `not(.simple)`, because when a
+ * simple list is nested inside another simple list, the inner list is not given
+ * a class. So instead we use two rules, one more specific than the other. */
+#pep-content ol li,
+#pep-content ul li {
+    margin: var(--paragraph-margin-vertical) 0;
+}
+#pep-content ol.simple li,
+#pep-content ul.simple li {
+    margin: 0 0;
+}
+
 /* Maths rules */
 sub,
 sup {