niri: set background and toggle (dark/light)

niri/.config/niri/config.kdl

@@ -321,3 +321,5 @@ binds {
 
     Mod+Shift+P { power-off-monitors; }
 }
+
+include "dark.kdl"

niri/.config/niri/dark.kdl

@@ -0,0 +1,9 @@
+layout {
+    background-color "#414853"
+
+    focus-ring {
+        width 4
+        active-color "#5396c7"
+        inactive-color "#505050"
+    }
+}

niri/.config/niri/light.kdl

@@ -0,0 +1,3 @@
+layout {
+    background-color "#c0c1c2"
+}