Zookey

#root {
	-fx-background-color:  linear-gradient(lightgray, gray);
}

#btn1{
	-fx-background-color: radial-gradient(center 50% -40%, radius 200%, #00FFFF 45%, #00BFFF 50%);
    -fx-text-fill: black;
    -fx-font-size: 20px;
    -fx-padding: 5 30 5 30;
    

Zookey

import javafx.application.Application;
import javafx.geometry.Insets;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;
/**

Zookey

import javafx.application.Application;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.event.EventHandler;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.control.ListView;
import javafx.scene.input.MouseEvent;
import javafx.scene.layout.VBox;

Zookey

import javafx.application.Application;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.event.EventHandler;
import javafx.scene.Scene;
import javafx.scene.control.ListView;
import javafx.scene.input.MouseEvent;

import javafx.scene.layout.StackPane;

Zookey

import javafx.application.Application;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.event.EventHandler;
import javafx.scene.Scene;
import javafx.scene.control.ListView;
import javafx.scene.input.MouseEvent;

import javafx.scene.layout.StackPane;