build: refine docs config

Author: skypjack

docs/CMakeLists.txt

@@ -12,15 +12,10 @@ if(DOXYGEN_FOUND)
         GIT_SHALLOW 1
     )
 
-    FetchContent_GetProperties(doxygen-awesome-css)
-
-    if(NOT doxygen-awesome-css_POPULATED)
-        FetchContent_Populate(doxygen-awesome-css)
-        set(doxygen-awesome-css_INCLUDE_DIR ${doxygen-awesome-css_SOURCE_DIR})
-    endif()
-
+    FetchContent_MakeAvailable(doxygen-awesome-css)
+    
     set(DOXY_SOURCE_DIRECTORY ${EnTT_SOURCE_DIR}/src)
-    set(DOXY_CSS_DIRECTORY ${doxygen-awesome-css_INCLUDE_DIR})
+    set(DOXY_CSS_DIRECTORY ${doxygen-awesome-css_SOURCE_DIR})
     set(DOXY_DOCS_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR})
     set(DOXY_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR})