[fractal] Add css for code blocks

[Alejandro Domínguez <aledomu src gnome org>]

commit 6e98d2b7d7eac470155e833b8690f5d3aca1ea29
Author: Maximiliano Sandoval R <msandova protonmail com>
Date:   Tue Oct 13 01:38:58 2020 +0200

    Add css for code blocks

 fractal-gtk/res/app.css | 12 ++++++++++++
 1 file changed, 12 insertions(+)
---
diff --git a/fractal-gtk/res/app.css b/fractal-gtk/res/app.css
index c5ef1af4..287913f4 100644
--- a/fractal-gtk/res/app.css
+++ b/fractal-gtk/res/app.css
@@ -428,6 +428,18 @@ box.folded-history
   font-size: large;
 }
 
+.codeview {
+  border-radius: 5px;
+  padding: 6px;
+  font-family: monospace;
+  background-color: @text_view_bg;
+  color: @theme_text_color;
+}
+
+.codeview > text {
+  background: none;
+}
+
 #clip-container {
   border-radius: 6px;
 }