diff --git a/poky/documentation/ref-manual/ref-style.css b/poky/documentation/ref-manual/ref-style.css
index 7077e4b..622ceb8 100644
--- a/poky/documentation/ref-manual/ref-style.css
+++ b/poky/documentation/ref-manual/ref-style.css
@@ -1,4 +1,7 @@
 /*
+
+   SPDX-License-Identifier: CC-BY-2.0-UK
+
    Generic XHTML / DocBook XHTML CSS Stylesheet.
 
    Browser wrangling and typographic design by