Shadow DOM is a nice touch and in terms of isolating CSS definitions per-component, it does something beyond what most popular front frameworks can do. That sai

Shadow DOM is a nice touch and in terms of isolating CSS definitions per-component, it does something beyond what most popular front frameworks can do. That said, I know some developers don't even use the shadow DOM; you can use inline styles like some people do with React or you can use a centralized stylesheet for skinning and only write barebones CSS definitions as part of components.