I'm not much of a JS/TS/HTML/CSS person either. But if I think something looks off and it's something I care about, then I'll lose a day boning up on that thing.
To your point that you're not sure what to search for, I do the same thing I always do: I start searching for reference documentation, reading it, and augmenting that with whatever prominent code bases/projects I can find.
This motivates the question: if you're doing all this work to verify the LLM, is the LLM really saving you anytime?
After just a few weeks in this brave new world my answer is: it depends, and I'm not really sure.
I think over time as both the LLMs get better and I get better at working with them, I'll start trusting them more.
One thing that would help with that would be for them to become a lot less random and less sensitive to their prompts.