is there any documentation to create a button which is stick on UI and every page. eg. like vaadin chat box.
UI is of vertical layout. if a button is added to it takes entire pane at bottom.
It takes two answers to address this question.
1: You want a component that appears on every page. This is done by having one single MainView class that will act as parent element of each of your routed views. If you add your button in that MainView, every View that defines that MainView as parent layout will then have the button showing up. More information [here]
(https://vaadin.com/docs/v14/flow/routing/tutorial-router-layout.html)
2: you want your button to stick to a certain area like the chat always remains in the bottomright corner, that is usually pure CSS.
Try searching for CSS position fixed and you will quickly find out how to style your button so it always floats on the correct spot.