Documentation: remove dark color on title page and ...

add "HTML_COLORSTYLE = TOGGLE" so the documentation user can toggle
  dark and light display mode.

Enable search engine.

documentation/Doxyfile.in

@@ -802,6 +802,21 @@ HTML_FOOTER            = @CMAKE_CURRENT_SOURCE_DIR@/src/html_footer
 
 HTML_STYLESHEET        =
 
+# The HTML_COLORSTYLE tag can be used to specify if the generated HTML output
+# should be rendered with a dark or light theme.
+# Possible values are: LIGHT always generate light mode output, DARK always
+# generate dark mode output, AUTO_LIGHT automatically set the mode according to
+# the user preference, use light mode if no preference is set (the default),
+# AUTO_DARK automatically set the mode according to the user preference, use
+# dark mode if no preference is set and TOGGLE allow to user to switch between
+# light and dark mode via a button.
+# The default value is: AUTO_LIGHT.
+# This tag requires that the tag GENERATE_HTML is set to YES.
+
+# Note: since doxygen 1.9.5, may issue warnings when using older versions
+
+HTML_COLORSTYLE        = TOGGLE
+
 # If the HTML_ALIGN_MEMBERS tag is set to YES, the members of classes,
 # files or namespaces will be aligned in HTML using tables. If set to
 # NO a bullet list will be used.
@@ -1485,4 +1500,4 @@ DOT_CLEANUP            = YES
 # The SEARCHENGINE tag specifies whether or not a search engine should be
 # used. If set to NO the values of all tags below this one will be ignored.
 
-SEARCHENGINE           = NO
+SEARCHENGINE           = YES

documentation/src/index.dox

@@ -1,7 +1,7 @@
 /**
 
 \mainpage FLTK Programming Manual
-<TABLE BGCOLOR="#9f9f9f" CELLPADDING="8" CELLSPACING="0" SUMMARY="TITLE BAR" WIDTH="100%" BORDER="0">
+<TABLE CELLPADDING="8" CELLSPACING="0" SUMMARY="TITLE BAR" WIDTH="100%" BORDER="0">
 <TR>
   <TD><CENTER>
     \image html FL200.png
@@ -17,7 +17,7 @@
   </CENTER></TD>
 </TR>
 </TABLE>
-<TABLE BGCOLOR="#9f9f9f" CELLPADDING="8" CELLSPACING="0" SUMMARY="TITLE BAR" WIDTH="100%" BORDER="0">
+<TABLE CELLPADDING="8" CELLSPACING="0" SUMMARY="TITLE BAR" WIDTH="100%" BORDER="0">
 <TR>
   <TD>
     This software and manual are provided under the terms of the GNU
@@ -27,7 +27,7 @@
   </TD>
 </TR>
 </TABLE>
-<TABLE BGCOLOR="#9f9fef" CELLPADDING="8" CELLSPACING="0" SUMMARY="Table of Contents" WIDTH="100%" BORDER="0">
+<TABLE CELLPADDING="8" CELLSPACING="0" SUMMARY="Table of Contents" WIDTH="100%" BORDER="0">
 <TR>
   <TD ALIGN="LEFT" VALIGN="TOP">