Update to commons-skin-4.2.
diff --git a/src/site/site.xml b/src/site/site.xml
index b69aba8..5be5a76 100644
--- a/src/site/site.xml
+++ b/src/site/site.xml
@@ -26,6 +26,12 @@
     <href>https://commons.apache.org/proper/commons-rng/index.html</href>
   </bannerRight>
 
+  <skin>
+    <groupId>org.apache.commons</groupId>
+    <artifactId>commons-skin</artifactId>
+    <version>4.2</version>
+  </skin>
+
   <body>
     <head>
       <![CDATA[<script type="text/javascript" id="MathJax-script" async src="https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-mml-chtml.js">
@@ -47,6 +53,19 @@
     <menu name="User Guide">
       <item name="Contents" href="/userguide/index.html"/>
     </menu>
-
   </body>
+
+  <custom>
+    <!-- Custom properties controlling the commons-skin template. -->
+    <commonsSkin>
+      <!-- 
+        Convert preformatted source section tags to prettyprint:
+          <div class="source"><pre> to <div class="source"><pre class="prettyprint">
+      -->
+      <prettyPrintSourcePreTags>true</prettyPrintSourcePreTags>
+
+      <!-- Add the "linenums" class to the prettyprint enabled source tags -->
+      <prettyPrintLineNumbersEnabled>false</prettyPrintLineNumbersEnabled>
+    </commonsSkin>
+  </custom>
 </project>