That's going to be an interesting shift. There are numerous website having online walkthrough courses with videos, Quiz, and useful projects for the practice ad experience.
Some are free and some paid, here is list of popular free ones:
- Code School
- Code Academy (very good to begin with)
- General Assembly Dash
However, for web design specifically there are some extremely useful websites to grasp the fundamentals (HTML/CSS) which are:
- Learn Layout
- Don't Fear the Internet
- Webmaking 101
Apart from the above, there are some reference modern websites for web-design such as w3schools or MDN web docs by Mozilla that would be always be helpful along the way. I although suggest that you don't get use to w3schools, the concepts and designs there are only the basic ones which everybody uses for their websites and not really novel approaches and tricks you need to use for a real-life website.
I highly recommend css-tricks for seeing real-life css it is a well-known highly educational websites with tutorials and forums connecting web designers.
After all, Web-design would be mastered through practice and projects just like many other fields. Grasping new designs, new patterns and getting comfortable with techniques such as prototyping or user empathy are the real skills that make a web designer top-notch and remarkable.