chrome-extensions-samples/functional-samples/tutorial.custom-cursor/style.css

html {
  cursor:
    url('chrome-extension://__MSG_@@extension_id__/dino.png') 16 16,
    auto;
}

a {
  cursor:
    url('chrome-extension://__MSG_@@extension_id__/dino-pointer.png') 16 16,
    auto;
}