[ablomen]

It looks great at first glance. A big problem though is that it styles basic elements. If for example you want to use a <table>, <mark> or <nav> where it would make sense in a custom element you'll have to reset all the styles of the library before adding your own.

[spankalee]

If your custom elements put their internals in shadow roots they'll be protected from page styling.

[ablomen]

Sorry custom elements might have been the wrong term to use. I mean custom interfaces, say an image gallery or a realtime search box where you would use elements like buttons and input's in a different way then the usage this framework defines for you. Using a nav both in your header and sidebar is a different example where these are not good defaults