Issue #3435831 by yassrzg: Add mourning theme/mode

ui_suite_dsfr.ui_skins.themes.yml

@@ -12,3 +12,27 @@ dark:
   label: "Dark"
   key: data-fr-scheme
   target: html
+
+mourning_system:
+  label: "Mourning system"
+  key: data-fr-mourning
+  target: html
+  value: ''
+  dependencies:
+    - system
+
+mourning_light:
+  label: "Mourning light"
+  key: data-fr-mourning
+  target: html
+  value: ''
+  dependencies:
+    - light
+
+mourning_dark:
+  label: "Mourning dark"
+  key: data-fr-mourning
+  target: html
+  value: ''
+  dependencies:
+    - dark