content: import time
  
  from dash import Dash, Input, Output, html, callback, set_props
  
  from .utils import get_background_callback_manager
  
  background_callback_manager = get_background_callback_manager()
  handle = background_callback_manager.handle
  
  app = Dash(__name__, background_callback_manager=background_callback_manager)
  
  app.layout = html.Div(
      [
          html.Button("start", id="start"),
          html.Div(id="secondary"),
          html.Div(id="no-output"),
          html.Div("initial", id="output"),
          html.Button("start-no-output", id="start-no-output"),
      ]
  )
  
  
  @callback(
      Output("output", "children"),
      Input("start", "n_clicks"),
      prevent_initial_call=True,
      background=True,
      interval=500,
  )
  async def on_click(_):
      set_props("secondary", {"children": "first"})
      set_props("secondary", {"style": {"background": "red"}})
      time.sleep(2)
      set_props("secondary", {"children": "second"})
      return "completed"
  
  
  @callback(
      Input("start-no-output", "n_clicks"),
      prevent_initial_call=True,
      background=True,
  )
  async def on_click2(_):
      set_props("no-output", {"children": "started"})
      time.sleep(2)
      set_props("no-output", {"children": "completed"})
  
  
  if __name__ == "__main__":
      app.run(debug=True)
  