In the past, we had a style scheme chooser widget to help people find style schemes that look useful. It was fairly rudimentary and doesn’t fit how we’d like style scheme selection to work going forward. So in what will become GtkSourceView 5.4, I’ve added the GtkSourceStyleSchemePreview widget which you can use to preview a specific style scheme.
It allows you to create your own chooser like is seen in this screenshot of Text Editor.
As usual, you can try it for yourself with Text Editor Nightly and follow along for more timely updates here.