developer.mozilla.org
Design for developers - Learn web development | MDN
The idea of this module is to (re-)introduce developers to design thinking. They may not want to work as designers, but having some basic user experience and design theory is good for everyone involved in building websites, no matter what their role. At the very least, even the most technical, "non-designer" developer should understand design briefs, why things are designed as they are, and be able to get into the mindset of the user. And it'll help them make their portfolios look better.