add style to version changed in html docs

- italic text, like the default
- indent the block

docs/source/_static/default.css

@@ -519,3 +519,12 b' ul.keywordmatches li.goodmatch a {'
 div.figure {
     text-align: center;
 }
+
+div.versionchanged {
+  margin-left: 30px;
+  margin-right: 30px;
+}
+
+span.versionmodified {
+    font-style: italic;
+}