Reddit mentions of Know Your Onions: Web Design: Jet Propel Yourself into the Driving Seat of a Top-class Web Designer and Hurtle Towards Creative Stardom

There's a lot to learn in terms of user experience, user interaction, user interface, and graphic design and typography. Often, a design team that works on major sites/software will be multidisciplinary with differing design backgrounds working to compliment each other's skills.

However, a good understanding of Human, Computer Interaction principles is essential for every developer. This might be a good starting point: https://www.interaction-design.org/literature/book/the-encyclopedia-of-human-computer-interaction-2nd-ed/human-computer-interaction-brief-intro but there is a whole canon of work from HCI up to modern UX thinking.

For a quick UI design walk through you could try Know Your Onions, you might find some of it useful and much of it quite basic. https://www.amazon.co.uk/Know-Your-Onions-Web-Design/dp/9063693125

I'm a really big fan of Know Your Onions; it both serves to cover the basics of design, as well as some of the post-design process that often tends to be glossed over in other content.

There's a Web Design version as well.