diff --git a/books/free-programming-books-langs.md b/books/free-programming-books-langs.md
index 8ff0c0b85..8639cafe9 100644
--- a/books/free-programming-books-langs.md
+++ b/books/free-programming-books-langs.md
@@ -947,7 +947,7 @@ Books on general-purpose programming that don't focus on a specific language are
 * [Canvassing](https://web.archive.org/web/20160505010319/http://learnjs.io/canvassing/read/) *(:card_file_box: archived)*
 * [Code Guide: Standards for developing flexible, durable, and sustainable HTML and CSS](http://mdo.github.io/code-guide/) - Mark Otto
 * [CSS Animation 101](https://github.com/cssanimation/css-animation-101)
-* [CSS Notes for Professionals](http://goalkicker.com/CSSBook) - Compiled from StackOverflow Documentation (PDF)
+* [CSS Notes for Professionals](http://goalkicker.com/CSSBook) - Compiled from StackOverflow Documentation (PDF) (CC BY-SA)
 * [CSS Optimization Basics](https://github.com/frontenddogma/css-optimization-basics) – Jens Oliver Meiert
 * [CSS Transition vs CSS animation](https://www.freecodecamp.org/news/css-transition-vs-css-animation-handbook/) - Oluwatobi Sofela
 * [Dive Into HTML5](http://diveinto.html5doctor.com) - Mark Pilgrim ([PDF](http://mislav.net/2011/10/dive-into-html5/))