Frontend & browser·Storage and platform APIs
your page's stylesheet had no effect inside the widget because its DOM was in a separate tree.
Shadow DOM
Also calledshadow root, style encapsulation
An encapsulated subtree attached to an element, with its own scope for styles and ids that page CSS cannot reach into. It gives genuine isolation rather than the convention-based kind, which is why it underpins web components and embedded widgets. That isolation cuts both ways: theming requires explicit parts and custom properties, and selectors, forms and focus all behave differently across the boundary.