I made a plotly express choropleth_mapbox of US zip codes. Can I add a choropleth geometry that is the city boundary?

Below is the code to create a choropleth_mapbox of Zip Codes, but in addition, I want to add another choropleth from a shapefile that is only the boundaries of the city

'''

zip_map_fig = px.choropleth_mapbox(zips, geojson=zip_map_zips, locations='Zip Code', 
                                color='price', 
                                range_color=(1, 5), 
                                featureidkey='properties.Zip Code',
                                center={'lat':mkt_lat, 'lon':mkt_long}, 
                                labels={'price' : 'Price'}, 
                                mapbox_style='carto-positron', 
                                color_continuous_scale='blues',
                                opacity=0.3, 
                                zoom=9,
                                hover_data=['Zip Code'])
zip_map_fig.update_geos(fitbounds='locations', visible=True)

'''

The map below works well for the Zip Codes, but all I want to do is add another line (an empty shape) that shows the outline of the whole city.

I already have the shapefiles for the Zip Codes and the outline of the city.

I tried incorporating the city limit shapefile into the shapefile that is used to create the choropleth_mapbox, but it has no effect.

I know how to add a scattermapbox, but I just want to add another choropleth.

Is this possible?