For functional stuff, sure, but I don't think this is achievable within the UI domain. CSS rules have implementation details that change how you write it (some problems have workarounds), for example there's a documented set of issues in flex implementations maintained here: https://github.com/philipwalton/flexbugs

It might be practical and possible to become mainstream for some domains, but it's doubtful for others. The most practical solution for UI is visual regression testing across browsers.