JavaFX in-memory dynamic CSS file editing and applying

[Pedro Duque Vieira]

Not sure if I totally understand what you want but you can change the
values of CSS variables through code by setting inline styles on
components, via setStyle method.

Pardon the publicity but yesterday I just happened to mention exactly that
on one of my posts and might help you:
https://pixelduke.com/2018/10/14/fxribbon-version-1-2-released/

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Pedro Duque Vieira - https://www.pixelduke.com