Background-image in CSS not working in Phoenix 1.6

Where is anything about making copies of images like phoenix-HEGEN2FR.png which esbuild is making after adding:

watchers: [
    # Start the esbuild watcher by calling Esbuild.install_and_run(:default, args)
    esbuild:
      {Esbuild, :install_and_run,
       [
         :default,
         ~w(--sourcemap=inline --watch --loader:.jpg=file --loader:.png=file --loader:.gif=file --loader:.svg=file)
       ]}
  ]

Also, there is NOT A SINGLE MENTION about the background-image problem in CSS files in the docs you linked.

Please, try it on your own with the clean install of Pheonix 1.6. I mentioned all the steps to reproduce this issue a few comments above.