This lets you customize the look of the default skin for JavaFX (Caspian) to create all kinds of themes. In the end it generates a CSS file that you can attach to your Scene and it will apply to all controls in your application. With a little customization of the selectors in the generated file, you could make it apply on only certain named panels or controls. JavaFX CSS has the advanced feature of derived colors. These are colors that are lighter or darker versions of some named color. This is used extensively throughout the default Caspian skin which is how we are able to do color theming with CSS like Caspian Styler above does. When you are working with derived colors you often have a design from a designer with an absolute color in it like #EEEEEE and you want to know what the derivation percentage would be from your chosen base color. This calculator will help work that out for you. It will also show you that you have to be careful choosing your base color as not all colors can be created from all base colors.