Finding new things to challenge yourself can be difficult, especially the motivation to persue them. Learning to code has been something I have looked at a couple of times and I probably know more than most people, but being more competent is definitely on my wish list. A few links I want to check back to when I have more time to spend.
http://www.htmlgoodies.com/primers/html/article.php/3478131
http://www.w3schools.com/html/html_basic.asp
https://www.codecademy.com/courses/web-beginner-en-HZA3b/0/1?curriculum_id=50579fb998b470000202dc8b