Use the doxygen-awesome.css stylesheet for web page generation

For a more beautiful set of online API documentation.

.reuse/dep5

@@ -33,6 +33,11 @@ Files: src/3rdparty/kdbindings/genindex_array.h
 Copyright: 2021 Jeremy Burns
 License: MIT
 
+# doxygen awesome
+Files: docs/api/doxygen-awesome.css
+Copyright: 2021 - 2023 jothepro
+License: MIT
+
 # Flutter
 Files: tests/flutter_tests_embedder/tests_embedder.* examples/flutter/assets/* examples/flutter/macos/Runner/Configs/AppInfo.xcconfig examples/flutter/.metadata examples/flutter/macos/Runner/Assets.xcassets/* examples/flutter/macos/Runner.xcodeproj/* examples/flutter/macos/Flutter/* examples/flutter/macos/Runner.xcworkspace/* examples/flutter/macos/.gitignore examples/flutter/macos/Runner/Configs/*.xcconfig examples/flutter/macos/Runner/Base.lproj/MainMenu.xib examples/flutter/macos/Runner/DebugProfile.entitlements examples/flutter/macos/Runner/Info.plist examples/flutter/macos/Runner/Release.entitlements examples/flutter/windows/runner/resources/app_icon.ico examples/flutter/windows/runner/runner.exe.manifest
 Copyright: Copyright 2013-2014 The Flutter Authors

docs/api/Doxyfile.cmake

@@ -1328,7 +1328,7 @@ HTML_STYLESHEET        =
 # documentation.
 # This tag requires that the tag GENERATE_HTML is set to YES.
 
-HTML_EXTRA_STYLESHEET  =
+HTML_EXTRA_STYLESHEET  = @CMAKE_CURRENT_SOURCE_DIR@/doxygen-awesome.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