::before and ::after pseudo-elements to create complex surfaces. For more complex cases like you can use tuiSurfaceLayer directive to introduce more layers behind content. But that is mostly necessary for additional elements like input type="radio" or a video tag as seen in the examples on the main tab.
Styles to to be applied to the element:background , border-radius , box-shadow , mask , padding , transform
Styles to be applied to ::BEFORE pseudo-element:backdrop-filter
Styles to be applied to ::AFTER pseudo-element: Any overlays on top of backdrop-filter effect of ::BEFORE pseudo-element