Fine-tuning joint area on choropleth map (Unwanted border line)

[tsuga324]

I’m creating a choropleth map and want to remove border lines from polygons.
I tried to make the marker line transparent, but I’m still seeing the line (apparently, 1 px overlap of polygon fills).

Is there any way to fix this?

import pandas as pd
import plotly.express as px

df = pd.DataFrame({'fips': ['01001', '01002'], 'test_value': [2, 2]})

geojson = {'type': 'FeatureCollection', 'features': [{
    'id': '01001',
    'type': 'Feature',
    'properties': {},
    'geometry': {'type': 'Polygon',
                 'coordinates': [[
                     [286.0241925716400, 40.77207562584153], 
                     [286.0244929790497, 40.77207562584153],
                     [286.0244929790497, 40.77230312801631], 
                     [286.0241925716400, 40.77230312801631],
                     [286.0241925716400, 40.77207562584153]]]},
    }, {
    'id': '01002',
    'type': 'Feature',
    'properties': {},
    'geometry': {'type': 'Polygon',
                 'coordinates': [[
                     [286.0244929790497, 40.77217562584153], 
                     [286.0247933864594, 40.77217562584153],
                     [286.0247933864594, 40.77240312801631], 
                     [286.0244929790497, 40.77240312801631],
                     [286.0244929790497, 40.77217562584153]]]},
    }]}

fig = px.choropleth_mapbox(df, geojson=geojson, locations='fips',
    color='test_value', color_continuous_scale='Turbo', range_color=(0, 12),
    opacity=0.3, labels={'test_value': 'Test value'},
    zoom=19.5, center={'lat': 40.77218937692893, 'lon': 286.0244929790497},  
    mapbox_style='light',
    )
fig.update_traces(marker_line_color='rgba(255,255,255,0)', selector=dict(type='choroplethmapbox')) #make the border transparent
fig.update_layout(margin={'r': 0, 't': 0, 'l': 0, 'b': 0})
fig.show()

Result:

I also tried to make the polygons slightly smaller. It seems okay when zoomed in, but the unwanted border line appears when zoomed out.

for idx, p in enumerate(geojson["features"]):
    poly = Polygon(p["geometry"]["coordinates"][0])
    poly = shapely.affinity.scale(poly, 0.992, 0.992, 1.0, "center")
    geojson["features"][idx]["geometry"]["coordinates"][0] = list(poly.exterior.coords)

df = pd.DataFrame({'fips': ['01001', '01002'], 'test_value': [2, 2]})

fig = px.choropleth_mapbox(df, geojson=geojson, locations='fips',
    color='test_value', color_continuous_scale='Turbo', range_color=(0, 12),
    opacity=0.3, labels={'test_value': 'Test value'},
    zoom=17.0, center={'lat': 40.77218937692893, 'lon': 286.0244929790497},  
    mapbox_style='light',
    )
fig.update_traces(marker_line_color='rgba(255,255,255,0)', selector=dict(type='choroplethmapbox')) #make the border transparent
fig.update_layout(margin={'r': 0, 't': 0, 'l': 0, 'b': 0})
fig.show()