Problem with dropdown for a map


I am trying to learn using Dash by following those codes:

I am currently doing exercise 4. I wanted to change a dropdown menu for “Choose Borroughs:” from a multiple choice to a single choice. I changed dcc.Checklist into dcc.Dropdown and then lines 139-140 into:

#labelStyle={‘display’: ‘inline-block’}

and then line 220 into:

Input(‘boroughs’, ‘value’)])

however after it, even though a dropdown menu looks like I wanted, the map disappears. I looked through the internet and can not find a solution for my issue.