Fold indicator styling via CSS not working

From the documentation in LineNumberFactory class, I should be able to change the fold indicator ("+")  styling using the CSS class ".fold-indicator". I tried doing that but nothing changed. Here is my styling

`.fold-indicator{
      -fx-text-fill: green;
}`

and I also tried

`.fold-indicator{
      -fx-fill: green;
}`
 But it doesn't still work. 