When I want to change the background colour of my TextArea in JavaFX (with CSS), many people recommend "-fx-control-inner-background". But when I look up the Oracle's CSS reference there's no such a thing as "-fx-control-inner-background"! In fact nowhere, in the Internet I could find a reference on that and yet it works!
My question is where do these people discover this information? Why, for example, isn't -fx-background-color working instead?
On
Note that -fx-control-inner-background is not a CSS property, but a "looked-up color" (essentially a CSS variable) that is defined in the default stylesheet, modena.css.
To the best of my knowledge, there's no official documentation that describes the looked-up colors used by modena. The only resource I know for finding these is the source code, which quite carefully documents the purpose and use of these variables.
It is valid to be concerned about back-compatibility when relying on undocumented functionality. I'd make the following arguments, that alleviate this concern to some extent:
The call
setUserAgentStylesheet(Application.STYLESHEET_MODENA);
in the Application subclass will ensure that modena is used as the default stylesheet, so if a new default stylesheet is defined for future JavaFX releases, this code will future-proof your application, under the "de-facto API" assumption in the previous bullet point. (Note this also gives the JavaFX team a way forward to create a new stylesheet without breaking existing code, which I think strengthens the "de-facto API" argument.)
So, on balance, I think relying on the looked-up colors that you can find in the modena.css source code is a safe approach.
On
Modena has become the default skin for JavaFX applications.
%HOMEPATH% on Windows is: C:\Users\USERNAME
The default maven directory is %HOMEPATH%\.m2\repository
And JavaFX can be found under %HOMEPATH%\.m2\repository\org\openjfx
Since JavaFX (OpenJFX) became modular the directory and file structure has changed. The most recent JavaFX version (as of this writing 19) has placed the CSS at %HOMEPATH%\.m2\repository\org\openjfx\javafx-controls\19 the CSS file can be found inside the following .jar file: javafx-controls-19-win.jar (platform specific)
I have extracted the whole modena folder and put it on GitHub: https://github.com/Remzi1993/OpenJFX-modena
And for anyone who is only interested in the core modena.css here is a public gist: https://gist.github.com/Remzi1993/23350e22a51d325ed00171c117fb66d4
You can also find out by going to their GitHub repo: https://github.com/openjdk/jfx/ and the specific directory: https://github.com/openjdk/jfx/tree/master/modules/javafx.controls/src/main/resources/com/sun/javafx/scene/control/skin (The structure might change in the future). They seem to have officially moved to GitHub (finally) and the most recent documentation is also moved to their website at https://openjfx.io
https://openjfx.io/openjfx-docs/
https://openjfx.io/javadoc/19/javafx.graphics/javafx/scene/doc-files/cssref.html
I finally found out something useful that shifts my understanding of FXML CSS.
According to this reference, each node in the scene graph can have substructures. For example in our case, TextArea has a substructure called content. It's this content that we should be looking to change and not the entire textarea. In this case:
works perfectly for me. In other words, we have a region (called content) drawn on the main node (textarea).
This also shows why many people would get only a, for example, red border when they try to change the background of an textarea to red. It's because that narrow border is the only part beneath the content visible to us.
Hope this helps ...