Grainger Sr. Software Engineer interview questions

Recruiter call, meet with Hiring Manager, System Design interview, and Full Stack Interview. Overall, it was easy until the full stack portion where they asked CSS stuff. I only have a little knowledge about CSS because usually we have a separate team that deals with that. Apparently that was enough to not move forward. They also said my full stack app (that I had to create before the interview) had fundamental Spring Boot issues, even though I’ve used the same principles and annotations I’ve been using for the last 4 years as a software engineer. Usually I understand the feedback I get but I was greatly disappointed this time.