A DESCRIPTION OF THE PROBLEM :
Currently, the only way to set the background color of a text segment in RichTextArea or CodeArea is through Java code, using RichParagraph.Builder#addHighlight(int start, int length, Color color).

However, one of the key strengths of JavaFX is its support for CSS-based styling, which allows developers to style components without writing code. Among the most fundamental aspects of text styling are foreground and background colors, both of which have been supported since CSS1 (1996).

Therefore, I propose adding support for styling background color of text via CSS. This is an essential and widely expected feature.