doc: change color of doctag on night mode

Fixes: #38641

PR-URL: #38652
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Derek Lewis <DerekNonGeneric@inf.is>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Zijian Liu <lxxyxzj@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

doc/api_assets/hljs.css

@@ -36,7 +36,8 @@
 }
 
 .dark-mode .hljs-keyword,
-.dark-mode .hljs-attribute {
+.dark-mode .hljs-attribute,
+.dark-mode .hljs-doctag {
   color: #66d9ef;
 }