vim/colorizer: use foreground mode

It's easy to confuse the background mode with search highlights.

config/nvim/lua/fschauen/plugins/colorizer.lua

@@ -8,9 +8,11 @@ M.event = {
 }
 
 M.config = function()
-  require('colorizer').setup(nil, {
-    css = true,
+  require('colorizer').setup(--[[ filetypes ]] nil, {
+    css  = true,             -- Enable all CSS features: rgb_fn, hsl_fn, names, RGB, RRGGBB
+    mode = 'foreground',
   })
 end
 
 return M
+