Hmm, you'd still have to ensure that your selector has higher specificity, right? That itself can be hard unless you're okay with adding !important to everything. I was thinking that inherit: none would somehow address this, but the rules would probably be pretty complicated.
You just apply that to each property you want to reset. You might think that applying it to EVERY property is a nightmare but in many cases you wouldnt need to. Disqus, for example, operates in your own CSS so it can look native to the page. They only have to override a few properties to assure their layout is good.
So yeah, while `inherit:none` would be awesome, I think `prop: initial` gets us most of the way there.
Also related: https://github.com/premasagar/cleanslate