I'm not sure "building a web browser" is such a great test for an LLM. It helps confirm that they can handle large codebases. But the actual logic in the browser engine will be based very heavily on Chromium/Firefox etc.
Agreed! I assume the reason for the forgetting of the features is that at least some were poorly supported when first released so developers create workarounds that then become the de facto standard.
It has been amazing to see the speed up in release and support of new CSS features over the last couple of years! Even the masonry layout has finally reached an experimental stage