What’s the Best Way to Learn Frontend Development for a Backend Engineer?

I'm an experienced backend engineer looking to dive into frontend development and I really want to do it right without relying on AI for help. If you were in my shoes, how would you approach learning the fundamentals of frontend applications? What topics would you prioritize first, and what lessons have you learned along the way that might not be obvious initially? Also, how did you figure out how to structure frontend code effectively? I'd appreciate any insights or suggestions! Just to give some background, I'm not completely new to frontend concepts like HTML, CSS, and libraries, but I often find it difficult to piece everything together to create a cohesive application. My aim is to develop my skills from scratch and tackle small projects to practice building and solving real issues. I'm looking for a balance between understanding the little details like centering a div and creating a solid frontend architecture for future projects.