Content Panel and Preview Window fail to visualise CSS edits from Style Sheet attached using Preview > Scene Style Sheets > Add a Style Sheet...

Open attached Button.FXML
Choose Preview > Scene Style Sheets > Add a Style Sheet... and add attached Button.css
Open the Button.css in your editor of choice and edit the -fx-background-color value - BUG - SB Content Panel and Preview Window will not show any edits. You have to close and re-open the document.