StyleScheme contains all the text styles to be used in [class@View] and [class@Buffer]. For instance, it
contains text styles for syntax highlighting, it may contain foreground and background color for non-highlighted text, color for the line
numbers, current line highlighting, bracket matching, etc.
Style schemes are stored in XML files. The format of a scheme file is documented in the [style scheme reference](./style-reference.html).
The two style schemes with IDs "classic" and "tango" follow more closely the GTK theme (for example for the background color).