When showing an image on, say, a button, it is not yet possible to style the size of the image.

Images on buttons are shown by using an ImageView as the graphic of a button as in

button.setGraphic(new ImageView(aPictureOfKevinReadingThisJiraIssue);

However, if you look at the docs found here

https://docs.oracle.com/javase/8/javafx/api/javafx/scene/doc-files/cssref.html#pane

ImageView does not support sizing properties such as -fx-pref-width, -fx-min-width, -fx-max-width.

I believe this feature is important because the size of an image shown might very well depend on the style sheet used. I would like to let my users pick between several style sheets, so people with reading disabilities can choose a style sheet with larger fonts and images. That will require me to style the images larger in my readability.css file.