Stage style is the way your window is decorated outside of the Scene.

You can control how Stage will look using StageStyle enum values. It can be passed to the constructor or through the initStyle() method:

// chapter1/StageStylesDemo
Stage stage = new Stage(StageStyle.UNDECORATED)
// or
stage.initStyle(StageStyle.TRANSPARENT)

See the existing options in the following figure. Note that a Windows screenshot was used here, but decorations will look different on other operating systems because they are a part of the OS user interface and not drawn by Java or JavaFX.