slideout.css

/** file: slideout.css
    place in same directory as SlideOut.java */
.root  {
  -fx-background-color: rgb(32, 32, 32);
  -fx-font-size: 20;
  -fx-padding: 10;
}

.sidebar {
  -fx-padding: 10 10 10 10;
  -fx-background-insets: 0 10 0 0;
  -fx-border-insets: 0 10 0 0;
  -fx-background-color: rgb(46,48,50);
  -fx-border-color: rgb(30, 30, 30);
  -fx-border-width: 2;
}

/** icons from: http://www.customicondesign.com (free for non-commercial use). */
.hide-left {
  -fx-graphic: url('http://www.veryicon.com/icon/64/Business/Pretty%20Office%205/Hide%20left.png');
}
.show-right {
  -fx-graphic: url('http://www.veryicon.com/icon/64/Business/Pretty%20Office%205/Hide%20right.png');
}

SlideOut.java

package slideout;

import javafx.animation.*;
import javafx.application.Application;
import javafx.event.*;
import javafx.geometry.Pos;
import javafx.scene.*;
import javafx.scene.control.*;
import javafx.scene.layout.*;
import javafx.scene.text.Text;
import javafx.scene.web.WebView;
import javafx.stage.Stage;
import javafx.util.Duration;

/** Example of a sidebar that slides in and out of view */
public class SlideOut extends Application {

    public static void main(String[] args) throws Exception { launch(args); }
    public void start(final Stage stage) throws Exception {
        stage.setTitle("Slide out YouTube demo");

        // create a sidebar with some content in it.
        final Pane lyricPane = createSidebarContent();
        SideBar sidebar = new SideBar(250, 100, lyricPane);
        VBox.setVgrow(lyricPane, Priority.ALWAYS);

        // layout the scene.
        final BorderPane layout = new BorderPane();
        Pane mainPane = new VBox(
                        sidebar.getControlButton());
        layout.setLeft(sidebar);
        layout.setCenter(mainPane);

        // show the scene.
        Scene scene = new Scene(layout);
        scene.getStylesheets().add(getClass().getResource("slideout.css").toExternalForm());
        stage.setScene(scene);
        stage.show();
    }

    private BorderPane createSidebarContent() {// create some content to put in the sidebar.


        final BorderPane lyricPane = new BorderPane();
        // Add Something

        return lyricPane;
    }

    /** Animates a node on and off screen to the left. */
    class SideBar extends VBox {
        /** @return a control button to hide and show the sidebar */
        public Button getControlButton() { return controlButton; }
        private final Button controlButton;

        /** creates a sidebar containing a vertical alignment of the given nodes */
        SideBar(final double expandedWidth, final double hiddenWidth, Node... nodes) {
            getStyleClass().add("sidebar");
            this.setPrefWidth(expandedWidth);
            this.setMinWidth(0);

            // create a bar to hide and show.
            setAlignment(Pos.CENTER);
            getChildren().addAll(nodes);

            // create a button to hide and show the sidebar.
            controlButton = new Button("Collapse");
            controlButton.getStyleClass().add("hide-left");

            // apply the animations when the button is pressed.
            controlButton.setOnAction(new EventHandler<ActionEvent>() {
                @Override public void handle(ActionEvent actionEvent) {
                    // create an animation to hide sidebar.
                    final Animation hideSidebar = new Transition() {
                        { setCycleDuration(Duration.millis(250)); }
                        protected void interpolate(double frac) {
                            if(frac < 1 - (hiddenWidth / expandedWidth) ) {
                                final double curWidth = expandedWidth * (1.0 - frac);
                                setPrefWidth(curWidth);
                            }
                        }
                    };
                    hideSidebar.onFinishedProperty().set(new EventHandler<ActionEvent>() {
                        @Override public void handle(ActionEvent actionEvent) {
                            controlButton.setText("Show");
                            controlButton.getStyleClass().remove("hide-left");
                            controlButton.getStyleClass().add("show-right");
                        }
                    });

                    // create an animation to show a sidebar.
                    final Animation showSidebar = new Transition() {
                        { setCycleDuration(Duration.millis(250)); }
                        protected void interpolate(double frac) {
                            if(frac > (hiddenWidth / expandedWidth) ) {
                                final double curWidth = expandedWidth * frac;
                                setPrefWidth(curWidth);
                                // setTranslateX(-expandedWidth + curWidth);
                            }
                        }
                    };
                    showSidebar.onFinishedProperty().set(new EventHandler<ActionEvent>() {
                        @Override public void handle(ActionEvent actionEvent) {
                            controlButton.setText("Collapse");
                            controlButton.getStyleClass().add("hide-left");
                            controlButton.getStyleClass().remove("show-right");
                        }
                    });

                    if (showSidebar.statusProperty().get() == Animation.Status.STOPPED && hideSidebar.statusProperty().get() == Animation.Status.STOPPED) {
                        if (getPrefWidth() == expandedWidth) {
                            hideSidebar.play();
                        } else {
                            showSidebar.play();
                        }
                    }
                }
            });
        }
    }
}

SlideOut with added utility of keeping the slidepane visible width. This can be used to show few controls of the slidepane in a minimized way.

Also contains DARK theme.