DatePickerSingle with Additional Frame

Screen Shot 2020-02-09 at 10.35.36 PM

Could you please help to remove the additional frame in the picture?
I copied the code from dash website: https://dash.plot.ly/dash-core-components/datepickersingle
But I’m not sure why I always get this additional frame.

I’m new to dash and frontend developing. Really appreciate your help!
Thanks!