Customize Doxygen output

* Generate new header.html for version 1.8.17
* Generate new stylesheet.css

Signed-off-by: Nikhil Raj <nikhil.raj@arm.com>
Change-Id: I7570789cb9ab324bbd385e839b1acca828c2403b
diff --git a/docs/Doxyfile b/docs/Doxyfile
index c58cfea..e7e7457 100644
--- a/docs/Doxyfile
+++ b/docs/Doxyfile
@@ -1180,7 +1180,7 @@
 # of the possible markers and block names see the documentation.
 # This tag requires that the tag GENERATE_HTML is set to YES.
 
-HTML_HEADER            = ./docs/header.xhtml
+HTML_HEADER            = ./docs/header.html
 
 # The HTML_FOOTER tag can be used to specify a user-defined HTML footer for each
 # generated HTML page. If the tag is left blank doxygen will generate a standard
@@ -1215,7 +1215,7 @@
 # list). For an example see the documentation.
 # This tag requires that the tag GENERATE_HTML is set to YES.
 
-HTML_EXTRA_STYLESHEET  = ./docs/stylesheet.css
+HTML_EXTRA_STYLESHEET  = ./docs/customdoxygen.css
 
 # The HTML_EXTRA_FILES tag can be used to specify one or more extra images or
 # other source files which should be copied to the HTML output directory. Note