[gtksourceview] css: increase border radius of GtkSourceStyleSchemePreview

[Christian Hergert <chergert src gnome org>]

commit 90642af0d63c1892766e5cc4ddd147b512d94772
Author: Christian Hergert <chergert redhat com>
Date:   Tue Oct 12 11:45:26 2021 -0700

    css: increase border radius of GtkSourceStyleSchemePreview
    
    This is closer to the design, which uses more radius than GtkFrame.

 gtksourceview/GtkSourceView.css | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/gtksourceview/GtkSourceView.css b/gtksourceview/GtkSourceView.css
index 2ae9da03..d8974edf 100644
--- a/gtksourceview/GtkSourceView.css
+++ b/gtksourceview/GtkSourceView.css
@@ -150,6 +150,7 @@ GtkSourceAssistant.informative.question image {
 
 GtkSourceStyleSchemePreview frame {
   margin: 1px;
+  border-radius: 11px;
 }
 GtkSourceStyleSchemePreview.selected frame {
   border-color: @theme_selected_bg_color;