Update index.html with contrast-color reference q

Added a reference to a contrast-color function and a video link.

Author: stopsopa

pages/css/index.html

@@ -68,6 +68,8 @@ <h2>Learn</h2>
 
         <script type="editor" data-lang="css" data-w="95%">
 
+          contrast-color(): rom: https://youtu.be/XVasJ3
+
           # from: https://youtu.be/XVasJ3shTYo?t=58
           - container queries
           - :has() selector