RFR: 8207328: API docs for javafx.css.Stylesheet are inaccurate / wrong

[Selim Dincer]

Hey,

Please review the fix for https://bugs.openjdk.java.net/browse/JDK-8207328

Pull request:
https://github.com/javafxports/openjdk-jfx/pull/147

Thanks,
Selim