diff --git a/doc/guides/custom.css b/doc/guides/custom.css
index c87c606119..221024655c 100644
--- a/doc/guides/custom.css
+++ b/doc/guides/custom.css
@@ -1,3 +1,7 @@
+/* SPDX-License-Identifier: BSD-3-Clause
+ * Copyright 2018 Mellanox Technologies, Ltd
+ */
+
 /* Override readthedocs theme */
 
 /* Spacing before a list item must be bigger than spacing inside the item.