Example of using new Pseudoclass API in JavaFX 8.

PseudoClassExample.java

package pseudoclasstest;

import java.util.HashMap;
import java.util.Map;
import java.util.regex.Pattern;

import javafx.application.Application;
import javafx.beans.binding.Bindings;
import javafx.beans.property.BooleanProperty;
import javafx.beans.property.SimpleBooleanProperty;
import javafx.beans.value.ObservableValue;
import javafx.collections.FXCollections;
import javafx.collections.ObservableMap;
import javafx.css.PseudoClass;
import javafx.geometry.HPos;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.ComboBox;
import javafx.scene.control.Label;
import javafx.scene.control.TextField;
import javafx.scene.layout.ColumnConstraints;
import javafx.scene.layout.GridPane;
import javafx.stage.Stage;

public class PseudoClassExample extends Application {

    @Override
    public void start(Stage primaryStage) {
        // Layout stuff (should be in FXML):
        final GridPane root = new GridPane();
        final TextField cityField = new TextField();
        final ComboBox<String> countryCombo = new ComboBox<>();
        final Label phoneFormatLabel = new Label();
        phoneFormatLabel.setId("phone-format");
        final TextField phoneField = new TextField();
        phoneField.setId("phone-field");

        final Button button = new Button("OK");
        root.addRow(0, new Label("City:"), cityField);
        root.addRow(1, new Label("Country:"), countryCombo);
        root.addRow(2, new Label("Telephone:"), phoneField, phoneFormatLabel);
        root.addRow(3, new Label(), button);

        ColumnConstraints leftCol = new ColumnConstraints();
        ColumnConstraints rightCol = new ColumnConstraints();
        leftCol.setHalignment(HPos.RIGHT);
        rightCol.setHalignment(HPos.LEFT);
        root.getColumnConstraints().addAll(leftCol, rightCol);

        // Controller stuff:
        final ObservableMap<String, String> formats = FXCollections.observableHashMap();
        formats.put("UK", "(01234) 123456");
        formats.put("USA", "(123) 456-7890");
        final Map<String, Pattern> regexps = new HashMap<>();
        regexps.put("UK", Pattern.compile("\\(0[1-9]\\d{2,5}\\)\\s*[1-9]\\d{5,}"));
        regexps.put("USA", Pattern.compile("\\([1-9]\\d{2}\\)\\s*\\d{3}-\\d{4}"));

        countryCombo.getItems().addAll(formats.keySet());
        countryCombo.getSelectionModel().select(0);

        phoneFormatLabel.textProperty().bind(
            Bindings.concat("Format: ",
                Bindings.stringValueAt(formats, countryCombo.valueProperty())));

        final PseudoClass invalidClass = PseudoClass.getPseudoClass("invalid");

        final BooleanProperty valid = new SimpleBooleanProperty();
        valid.bind(Bindings.createBooleanBinding(
                () -> regexps.get(countryCombo.getValue()).matcher(phoneField.getText()).matches(),
                countryCombo.valueProperty(), phoneField.textProperty()));
        final ObservableValue<Boolean> invalid = valid.not();

        invalid.addListener((obs, oldValue, newValue) -> root.pseudoClassStateChanged(invalidClass, invalid.getValue()));
        root.pseudoClassStateChanged(invalidClass, invalid.getValue());

        button.disableProperty().bind(invalid);

        // Application stuff:
        Scene scene = new Scene(root, 480, 260);
        scene.getStylesheets().add(getClass().getResource("pseudoClassTest.css").toExternalForm());
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    public static void main(String[] args) {
        launch(args);
    }
}

pseudoClassTest.css

.root {
	-fx-padding: 10px ;
	-fx-hgap: 5px ;
	-fx-vgap: 5 px ;
}

.root:invalid #phone-field {
	-fx-background-color: red  ;
}
.root:invalid #phone-format {
	-fx-text-fill: red ;
}