Use the -rtfx prefix for RichTextFX specific underline properties, us…

[afester]

…e the underline width as the toggle to enable/disable the underline

[TomasMikula]

Cool, thanks!

[JordanMartinez]

I've updated the CSS guide to use the updated prefix.

[TomasMikula]

Great, thanks @JordanMartinez !

[JordanMartinez]

No problem!

Quick question @TomasMikula TextExt also has the CSS property -fx-background-fill. Could you clarify: is this used internally (and thus shouldn't be included in the guide) or another part of the text that can be styled (and thus should be in the guide and also use the -rtfx prefix)?

[TomasMikula]

Good catch! It is meant to be used by users. So it should be renamed to -rtfx and included in the guide. At that occasion, we might as well rename it to -rtfx-background-color, since the only reason it was called -fill instead of -color was JDK-8133685.