diff -r 5af9fa90cd7b -r 48b88b9c11eb src/jdk.javadoc/share/classes/jdk/javadoc/internal/doclets/formats/html/SingleIndexWriter.java
--- a/src/jdk.javadoc/share/classes/jdk/javadoc/internal/doclets/formats/html/SingleIndexWriter.java	Wed Nov 27 12:18:40 2019 +0100
+++ b/src/jdk.javadoc/share/classes/jdk/javadoc/internal/doclets/formats/html/SingleIndexWriter.java	Wed Nov 27 13:08:16 2019 +0100
@@ -28,6 +28,8 @@
 import java.util.Set;
 import java.util.TreeSet;
 
+import jdk.javadoc.internal.doclets.formats.html.markup.BodyContents;
+import jdk.javadoc.internal.doclets.formats.html.markup.ContentBuilder;
 import jdk.javadoc.internal.doclets.formats.html.markup.Entity;
 import jdk.javadoc.internal.doclets.formats.html.markup.HtmlStyle;
 import jdk.javadoc.internal.doclets.formats.html.markup.HtmlTag;
@@ -95,15 +97,10 @@
     protected void generateIndexFile() throws DocFileIOException {
         String title = resources.getText("doclet.Window_Single_Index");
         HtmlTree body = getBody(getWindowTitle(title));
-        HtmlTree header = HtmlTree.HEADER();
-        addTop(header);
+        Content headerContent = new ContentBuilder();
+        addTop(headerContent);
         navBar.setUserHeader(getUserHeaderFooter(true));
-        header.add(navBar.getContent(true));
-        body.add(header);
-        HtmlTree main = HtmlTree.MAIN();
-        main.add(HtmlTree.DIV(HtmlStyle.header,
-                HtmlTree.HEADING(Headings.PAGE_TITLE_HEADING,
-                        contents.getContent("doclet.Index"))));
+        headerContent.add(navBar.getContent(true));
         HtmlTree divTree = new HtmlTree(HtmlTag.DIV);
         divTree.setStyle(HtmlStyle.contentContainer);
         elements = new TreeSet<>(indexbuilder.getIndexMap().keySet());
@@ -120,13 +117,18 @@
             }
         }
         addLinksForIndexes(divTree);
-        main.add(divTree);
-        body.add(main);
         HtmlTree footer = HtmlTree.FOOTER();
         navBar.setUserFooter(getUserHeaderFooter(false));
         footer.add(navBar.getContent(false));
         addBottom(footer);
-        body.add(footer);
+        body.add(new BodyContents()
+                .setHeader(headerContent)
+                .addMainContent(HtmlTree.DIV(HtmlStyle.header,
+                        HtmlTree.HEADING(Headings.PAGE_TITLE_HEADING,
+                                contents.getContent("doclet.Index"))))
+                .addMainContent(divTree)
+                .setFooter(footer)
+                .toContent());
         createSearchIndexFiles();
         printHtmlDocument(null, "index", body);
     }