How to style FXML-defined popups?

[Greg Brown]

> the following works as an FXML alternative to adding the stylesheet in Java code:
> 
>>  <stylesheets>
>>    <String fx:value="/the/fully/qualified/path/to/the/desired.css"/>
>>  </stylesheets>
> 
> It also requires this
> 
>> <?import java.lang.String?>
> 
> which was a bit unexpected. URL did not work here because it was not coerced to a string.

FYI, this was fixed in either 2.1 or 2.2, so the following should also work:

<stylesheets>
    <URL value="@desired.css"/>
<stylesheets>