I tried using the LineNumberFactory function to add line numbers but they only show as grayish rectangles How it looks

I tried to add the .lineno and .fold-indicator classes in my css file (like this)

.fold-indicator{
-fx-background-color:#292929;
}
.fold-indicator .lineno{
-fx-fill:#4a4a4a;
}

and change the background and text color but it didnt do anything. This is how my java code looks:

    private Node createTextAreaBox() {
 mainCodeArea = new CodeArea();
        mainCodeArea.setId("mainCodeArea");
        mainCodeArea.setParagraphGraphicFactory(LineNumberFactory.get(mainCodeArea));
 if(initialText){
            mainCodeArea.replaceText(textAreaText);
        }
        else{
            mainCodeArea.replaceText("");
        }
}

any ideas as to what could be wrong?