docs: improve the HTML formatting of kerneldoc comments

Make a few changes to cause functions documented by kerneldoc to stand out
better in the rendered documentation.  Specifically, change kernel-doc to
put the description section into a ".. container::" section, then add a bit
of CSS to indent that section relative to the function prototype (or struct
or enum definition).  Tweak a few other CSS parameters while in the
neighborhood to improve the formatting.

Acked-by: Mauro Carvalho Chehab <mchehab@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/sphinx-static/custom.css

@@ -10,5 +10,19 @@ div.body h3 { font-size: 130%; }
 
 /* Tighten up the layout slightly */
 div.body { padding: 0 15px 0 10px; }
-div.document { margin: 20px 10px 0 10px; }
 div.sphinxsidebarwrapper { padding: 1em 0.4em; }
+/* Tweak document margins and don't force width */
+div.document {
+    margin: 20px 10px 0 10px; 
+    width: auto;
+}
+
+/*
+ * Parameters for the display of function prototypes and such included
+ * from C source files.
+ */
+dl.function, dl.struct, dl.enum { margin-top: 2em; background-color: #ecf0f3; }
+/* indent lines 2+ of multi-line function prototypes */
+dl.function dt { margin-left: 10em; text-indent: -10em; }
+dt.sig-object { font-size: larger; }
+div.kernelindent { margin-left: 2em; margin-right: 4em; }