Update free-programming-interactive-tutorials-en.md (#6362)

* Update free-programming-interactive-tutorials-en.md

* Update free-programming-interactive-tutorials-en.md

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Co-authored-by: NDavid Ordás <3125580+davorpa@users.noreply.github.com>
Co-authored-by: NDavid Ordás <3125580+davorpa@users.noreply.github.com>

more/free-programming-interactive-tutorials-en.md

@@ -168,6 +168,7 @@
 * [HTML Tutorial](https://www.w3schools.com/html/) - W3Schools
 * [Knights of the Flexbox Table](https://knightsoftheflexboxtable.com)
 * [Learn by doing beginner projects](https://dash.generalassemb.ly)
+* [Learn CSS: an evergreen CSS course and reference to level up your styling expertise](https://web.dev/learn/css/) - Andy Bell, Rachel Andrew, Una Kravets, Adam Argyle, Rob Dodson, Jiwoong Lee et al. (web.dev)
 * [Learn HTML & CSS interactively](https://www.codecademy.com/learn/web)
 * [Prototyping a professional website](https://www.codecademy.com/learn/make-a-website)