scribble: adjust `subsubsub*section' font size

Closes PR 12868

original commit: b5189c823216fda8ea68b7254a2a4df5cc4ee5f3

collects/scribble/base.rkt

@@ -107,7 +107,7 @@
   (let ([content (decode-content str)])
     (make-paragraph plain 
                     (list
-                     (make-element 'bold
+                     (make-element "SSubSubSubSection"
                                    (if tag
                                        (make-target-element #f content `(part ,tag))
                                        content))))))

collects/scribble/scribble.css

@@ -38,6 +38,11 @@ h3, h4, h5, h6, h7, h8 {
   margin-bottom: 0.5em;
 }
 
+.SSubSubSubSection {
+  font-weight: bold;
+  font-size: 0.83em; /* should match h5; from HTML 4 reference */
+}
+
 /* Needed for browsers like Opera, and eventually for HTML 4 conformance.
    This means that multiple paragraphs in a table element do not have a space
    between them. */

collects/scribble/scribble.tex

@@ -154,6 +154,8 @@
 \newcommand{\subsectionhidden}[1]{\subsection{#1}}
 \newcommand{\subsubsectionhidden}[1]{\subsubsection{#1}}
 
+\newcommand{\SSubSubSubSection}[1]{{\bf #1}}
+
 % For hidden parts with an empty title:
 \newcommand{\notitlesection}{\vspace{2ex}\phantomsection\noindent}