Unless you're using non-standardized features, the web is supposed to be backward compatible. I can still look at pages written in the 90s just fine. The probl

Unless you're using non-standardized features, the web is supposed to be backward compatible. I can still look at pages written in the 90s just fine. The problem comes when you start using prefixed css keys or unstable / non standard features. Since those are sort of "WIP features", it should be obvious that they need to be maintained.