Styling default JavaFX Dialogs - javafx

Question

I'm looking for a way to style the default JavaFX Dialog (javafx.scene.control.Dialog).
I tried to get the DialogPane and add a stylesheet, but it covers only a small piece of the dialog. I would prefer to style only with an external css file and without to add styleClasses over the code. This would look messy (header, content, own content on the content and more..)
I googled already alot and only found examples for ControlsFX, but since jdk8_40 JavaFX has it's own Dialogs i use them now.
Any suggestions?
Edit:
Since José Pereda posted the solution i created my own dialog.css.
I'll post it here because it covers the whole dialog and maybe someone want's to copy&paste it. Note .dialog-pane is already a given styleClass name so you don't need to apply your own. Of course, Josés is more fine detailed.
.dialog-pane {
-fx-background-color: black;
}
.dialog-pane .label {
-fx-text-fill: white;
}
.dialog-pane:header .header-panel {
-fx-background-color: black;
}
.dialog-pane:header .header-panel .label {
-fx-font-style: italic;
-fx-font-size: 2em;
}

Answer 1

You can style your dialogs with your own css file, but for that you need to take into consideration that the dialog is in fact a new stage, with a new scene, and the root node is a DialogPane instance.
So once you create some dialog instance:
#Override
public void start(Stage primaryStage) {
Alert alert = new Alert(AlertType.CONFIRMATION);
alert.setTitle("Confirmation Dialog");
alert.setHeaderText("This is a Custom Confirmation Dialog");
alert.setContentText("We override the style classes of the dialog");
...
}
you can access to its dialog pane and add your own style sheet and your own class selector:
DialogPane dialogPane = alert.getDialogPane();
dialogPane.getStylesheets().add(
getClass().getResource("myDialogs.css").toExternalForm());
dialogPane.getStyleClass().add("myDialog");
Now the trick is knowing all the rules a Dialog style sheet has implemented by default.
And that's a difficult task... since they are not in the modena.css file, as for all the regular controls. On the contrary, they are found in the modena.bss file, a binary file located in the jfxrt.jar under private packages.
After some digging I've managed to get those rules, so your custom myDialogs.css file will look something like this:
.myDialog{
-fx-background-color: #f9d900;
}
.myDialog > *.button-bar > *.container{
-fx-background-color: #a9e200;
}
.myDialog > *.label.content{
-fx-font-size: 14px;
-fx-font-weight: bold;
}
.myDialog:header *.header-panel{
-fx-background-color: #a59c31;
}
.myDialog:header *.header-panel *.label{
-fx-font-size: 18px;
-fx-font-style: italic;
-fx-fill: #292929;
}
And you will have your styled dialog:
Note that being a bss file under private packages, these selectors can change without notice in future releases.
EDIT
I've just found that the .dialog-pane selector is already part of modena.css in the last 8u40 early versions, so you can find all the selectors and rules applied to the dialog pane there.