This is a sample web part that illustrates how to use PnPjs, the IntersectionObserver API, and CSS animations to build a SharePoint Framework client-side web part that adds reveal-on-scroll animations to other web parts on a modern SharePoint page.
Open this sample in the gallery (popup panel): Open in gallery
Source: https://github.com/pnp/sp-dev-fx-webparts/tree/main/samples/react-animpage