Add `Shade.nvim`.

lua/custom/plugins/shade.lua

@@ -0,0 +1,14 @@
+return {
+  "sunjon/Shade.nvim",
+  config = function()
+    require('shade').setup({
+      overlay_opacity = 50,
+      opacity_step = 1,
+      keys = {
+        -- brightness_up   = '<C-Up>',
+        -- brightness_down = '<C-Down>',
+        -- toggle          = '<Leader>s',
+      }
+    })
+  end
+}