[gtksourceview] css: fix borders for GtkSourceStyleSchemePreview

[Christian Hergert <chergert src gnome org>]

commit 99261fdcacad7e624378d6613a92c7bff1cfe35b
Author: Christian Hergert <chergert redhat com>
Date:   Tue Oct 12 11:06:53 2021 -0700

    css: fix borders for GtkSourceStyleSchemePreview

 gtksourceview/GtkSourceView.css | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
---
diff --git a/gtksourceview/GtkSourceView.css b/gtksourceview/GtkSourceView.css
index 4484b3a7..74391307 100644
--- a/gtksourceview/GtkSourceView.css
+++ b/gtksourceview/GtkSourceView.css
@@ -149,10 +149,12 @@ GtkSourceAssistant.informative.question image {
 }
 
 GtkSourceStyleSchemePreview frame {
-  border-width: 2px;
+  margin: 1px;
 }
 GtkSourceStyleSchemePreview.selected frame {
   border-color: @theme_selected_bg_color;
+  border-width: 2px;
+  margin: 0;
 }
 GtkSourceStyleSchemePreview.selected image {
   border-radius: 9999px;