6d5c5320d439d7d2623429f01f54c8e7a620edcd Release 2.4.0

Not going for a 3 release yet - there are other updates needed for that,
but this is to roll out dark mode

Sync to source repo @6d5c5320d439d7d2623429f01f54c8e7a620edcd

Author: AllanJard

datatables.json

@@ -14,5 +14,5 @@
     ],
     "src-repo": "http://github.com/DataTables/Buttons",
     "last-tag": "2.3.6",
-    "last-sync": "a966bcfc52407951dae447f088abdf20cb494148"
+    "last-sync": "6d5c5320d439d7d2623429f01f54c8e7a620edcd"
 }