The Resource interface and its implementations are the connections between Java code and resources such as images, downloadable files, or embedded content. You have probably used a StreamResource to dynamically generate a file that a user can download or a ThemeResource to display an image in your UI.

A theme, in turn, is a set of static resources used to configure the appearance of a Vaadin application. By default, Vaadin applications use the Valo theme, a powerful set of styles that can be configured using variables.