I've this style sheet:

.scene {
  /* My own color names */
  textcolor: darkgreen;
}
.label {
    -fx-text-fill: textcolor;
}
.styled-button {
    -fx-text-fill: white !important;
    -fx-font-size: 23;
}

but my button color is green, not white.

Source code:

package org.sepix.javafx.csstheming;

import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;

public class SmallCSS extends Stage {
  String style = "/org/sepix/javafx/csstheming/styles/small.css";
  /*
   .scene {
      textcolor: darkgreen;
    }

   .label {
      -fx-text-fill: textcolor;

    }
    .styled-button {
      -fx-text-fill: white !important;
      -fx-font-size: 23;
    }

   */

  public SmallCSS() {
    VBox vbox = new VBox();
    
    Scene scene = new Scene (vbox);
    scene.getStylesheets().add (style);
    
    Label label = new Label("A Label");
    
    Button button = new Button("Button");
    button.getStyleClass().add("styled-button");
    
    vbox.getChildren().addAll(label, button);
    
    setScene(scene);
  }
}