[gtk/ebassi/gidocgen] frame: Use markdown for css tree

[Matthias Clasen <matthiasc src gnome org>]

commit 8292ce21bb44995cc19c1f48c7d835a480c7cfb1
Author: Matthias Clasen <mclasen redhat com>
Date:   Sat Feb 27 19:47:15 2021 -0500

    frame: Use markdown for css tree

 gtk/gtkframe.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/gtk/gtkframe.c b/gtk/gtkframe.c
index 392fed5abf..4d99dc4312 100644
--- a/gtk/gtkframe.c
+++ b/gtk/gtkframe.c
@@ -69,11 +69,11 @@
  *
  * # CSS nodes
  *
- * |[<!-- language="plain" -->
+ * ```
  * frame
  * ├── <label widget>
  * ╰── <child>
- * ]|
+ * ```
  *
  * `GtkFrame` has a main CSS node with name “frame”, which is used to draw the
  * visible border. You can set the appearance of the border using CSS properties